I've been extensively researching the mirrorless options... with a strong emphasis on the Canon M5 because it can share lenses and other accessories (flash, wireless trigger, ?) with my Canon DSLR gear.
The problem with Canon mirrorless is the limited lens selection. To date, which is actually now five years in, they have a total of seven lenses. Two primes: 22mm f/2, 28mm Macro f/3.5. And five zooms: 11-22mm, 15-45mm, 18-55mm, 18-150mm, 55-200mm. Notice that three of those zooms duplicate a lot of focal lengths. Why have both a 15-45mm and 18-55mm, especially since those two even sell for the same price! The zooms are all relatively slow, variable aperture, too: f/3.5-6.3, f/4-5.6, f/4.5-6.3. There's rumor that there will be a 32mm f/1.4 introduced soon, but that's still just a rumor (and not a focal length I'm interested in).
All but one of the Canon EF-M lenses have IS (the 22mm). But all are STM (stepper motor) focus drive lenses. One of the complaints about Canon MILC has been slow autofocus. It's improved alot in the M5 and later models with the cameras' Dual Pixel Auto Focus (versus contrast detection in the earlier models), but still isn't as fast as a DSLR with USM lenses. I don't know why Canon has been so slow to develop lenses for the system. Nor do I know why they haven't offered faster USM (ultrasonic) focus drive lenses. Maybe USM makes for a bigger lens and that's their concern. Canon themselves claims USM is 2X to 4X faster focusing than STM, in the only lens they've offered using both (EF-S 18-135mm).
It's possible Canon and Nikon were slow to develop MILC systems because they were concerned about eroding their own DSLR sales. Of course, an argument can be made that by NOT committing to and quickly developing a competitive MILC system, Canon and Nikon ended up sending a lot of customers looking for cameras elsewhere (i.e., Sony, Fuji, Oly/Panasonic). Both Canon and Nikon treated their MILC like they were point-n-shoots with interchangeable lenses, while the other manufacturers seemed to think of MILC as "mini-DSLRs".
At least Canon made their MILC APS-C (like most Sony, Fuji, Pentax). Nikon took a further mis-step by using a smaller "CX" (1", 2.7X lens factor) sensor in their MILC system. That left the Nikon 1 system out in the wilderness on its own, with no support from third party manufacturers, which ultimately killed it. Canon was able to re-boot, thanks in part to sharing sensors, AF systems and other tech with their DSLRs. Both Canon and Nikon are promising "full frame MILC" to compete with Sony... but I'm not holding my breath.
M5 and M50 are two different cameras, though they both have similar electronic viewfinders and both use the same 24MP APS-C sensor. The M50 is the newer of the two, the first Canon camera to use a next-generation Digic 8 processor, first of the M-series to have 4K video and features a fully articulated LCD screen. Probably due to the newer processor, the M50 can shoot continuously slightly faster than the M5 (10 frames per second versus 9 fps). And the M50 has 143 focus points, where the M5 has 49. The M50 is slightly lighter than the M5, too... but only about 40 grams (10 paper clips).
The backs of the two models look almost identical. It's not much, but he M5's rear screen is slightly larger. It's tiltable, but less fully articulated. Check out top views of the two cameras... the M5 has more external controls for direct settings such as ISO, Exposure Compensation, and more. With the M50 you'll need to dive into the menu and using the rear screen to make more settings.
M50 is also using a new CR3 RAW file format. No problem if you just shoot JPEGs or if you use Canon's latest version of DPP with RAW from the camera. But it will require an update of any third party RAW conversion software you might be using.... And that may or may not be ready to support the new format yet (and there can be glitches once updates are made). The M5 uses CR2 that's supported by all current RAW converters, AFAIK.
Personally I wasn't interested in M-series until they implemented a built-in viewfinder. M5 does that. And, honestly, the way I want to use one, the lens selection isn't too much of a concern either. I don't plan to replace DSLRs with a MILC. The smaller size is important for the camera to be unobtrusive and a good travel companion. But that's not my main concern either.
Mainly I want to use the MILC much the way I did rangefinder cameras in the past... with a small kit of compact, fast, manual focus prime lenses. Those are available from third party manufacturers (take note, Canon!) I'd also like to be able to use some vintage lenses I have on it, via adapters. Those are also widely available for EF-M mount (Leica M-39, Konica K/AR, Canon FD/FL).
What keeps me from buying is that it's a "fun" camera for me, more than a "work" camera. Priorities! I also
really wish there were option to fit a vertical/battery grip... Both to increase battery capacity and to provide vertical/portrait orientation controls. I use grips on all my DSLRs. It's even more important on a MILC because they use smaller size batteries (LP-E17 in both these M-series) which give a lot fewer shots per charge. CIPA ratings are about 400 with M5, and about 350 shots with M50... though I can probably beat those estimates, I get upwards of 2500 shots per charge with my DSLRs (1200+ per battery). Both Sony and Fuji offer battery grips for some of their models. I wonder if Canon thinks buyers of these cameras won't want/need grips increasing the size and weight... so they haven't designed the cameras to accommodate them... the memory card slot location is a problem, plus there's no connectivity for controls. Canon also doesn't offer grips or provide option to fit one to a T7, T6, SL1, SL2 models. (There are third party grips for T6... and maybe T7.... but they are quite limited in vertical control functionality.)
BTW, Canon LP-E17 batteries are relatively expensive at around $55 apiece, best price I've found. There are cheaper third party, but I've heard and read that there have been a lot of issues with them in M-series cameras. At least for now, until they sort out any issues, I'd avoid them!
Another thing... I'm pretty sure the Canon M-series firmware and user interface are adapted from the G-series Powershots, rather than one brought over from the DSLRs.
In other words, even though there's been considerable improvement Canon seems to still be treating their APS-C format MILC a bit as amateurish cameras... As if they're not something a pro might want to use. IMO, that's a mistake!
It concerns me even more to hear all the talk of full frame mirrorless from them. I'm afraid they'll take resources away from further developing their APS-C models to focus on the FF and even with the FF models Canon (and Nikon) will make additional mistakes. Canon is in better shape than Nikon, who needs to go back to the drawing board to design a whole new system from the ground up and doesn't have some of the tech yet. Canon can use existing lens mounting, connectivity and focusing systems. I'm just afraid they will not do so.... that they'll come up with a fourth lens mount especially for the FF MILC cameras (EF, EF-S, EF-M and now EF-M FF). That would be a mistake, especially if they are as glacially slow and reticent developing it, as they have been with their EF-M series. There's little savings of size and weight with FF MILC... compare a Sony A7III or A7rIII with a Canon 6DII DSLR. So to me it would make more sense to simply design the FF MILC to use existing EF lenses instead. If nothing else, they should design a camera that has a semi-permanent, sturdy, but removable mounting interface that allows EF lenses to be used on the camera... without need for adapters. It could be done in a way that gave option to reconfigure the camera later to use a new line of EF-M FF lenses. I know it can be done. In fact Pentax produced a mirrorless that was designed to work with their legacy manual focus and existing AF DSLR lenses.... But the Pentax K-01 MILC was APS-C format and they never seemed to make very much effort to market it. (Push was on to make a FF DSLR, which had been rumored for years, ultimately and
finally the K1 and now K1 II. It probably didn't help that Pentax went through a couple ownership and management changes, likely effecting all their development, production and marketing.)
For what I want to do with a MILC, I don't need or want full frame. I prefer an APS-C model and would not want to see those continue to be treated as amateurish and neglected in favor of some new FF camera and lenses to use on it. It's happened before. Canon made the mistake of treating APS-C DSLRs as more amateur cameras, until Nikon woke them up with their D200 and then D300 models. Canon responded fairly quickly with the 7D series, which in a sense ended up "killiing off" their own APS-H 1D-series, but has proven quite successful.
No camera is perfect. The M5 does most of what I want. Although it still falls a little short, I still may get one... soon as I can justify dropping a chunk of money on a "fun" camera. Maybe if I win the lottery!
The M50 doesn't interest me, primarily because of the control interface. I'm not into video and don't want to have to do major updates to my post-processing software just to be able to work with one.
IF I were looking to replace my DSLRs completely and take fullest advantage of MILC size/weight advantages... I'd probably be looking at Fuji or Sony instead. Sony is currently the only game in town for full frame (well, except for Leica, but I'm not a millionaire
). The accessory options and lens selection of the Fuji system impresses me most of all the MILC... they're pricey, though. At least the lenses and cameras that interest me are. I can't help but wonder when they'll change the name from "Fujifilm" though.... now that their cameras are 100% digital!