I have one of these adapters that I use in Canon cameras. It is OK for single shot shooting, but is likely to fail writing when shooting events, sports, etc. in burst mode since the adapter is not likely to be fast enough during heavy writing to the card. I find this to be the case in my 7D2 which has a 10 shoots per second. It works OK with a few shoots at a time, but if you go at maximum for a over a second, I get writing errors.

I agree with the comments about the individual's requirements driving one's expectations around having 1 or 2 slots. When I shoot things where my reputation on the line, I want two slots and duplicate images. I know that I am fallible and capable of screwing up at times, especially in the "heat of the moment". I worry more about myself than the camera at times; I have never had a card fail to date, but I have had errors at times. I can understand the a pro's concerns about wanting mirrorless cameras to have multiple slots.

I started shooting in the mid 60's with a used range finder. I got my first SLR in the late 70's. I did my own B&W developing and printing with an auction purchased enlarger. Later I added Extachrome slide film developing as well. For me one of the biggest things that helped me advance in ability was not just the number of shots you could take with digital. One of the best things about digital is being able to go back and review the EXIF data. In the film days, the equivalent of EXIF data was the little pocket notebook and pen you carried along to write down your film type/speed, shutter speed and aperture. If you shot on aperture priority as opposed to manual, you might not know what your shutter speed was, so that probably didn't recorded in the notebook.

A couple of wedding preparation thoughts. I only shoot two or three weddings a year, so I don't know all of the local places for receptions and ceremonies. Prior to the reception I like to go the the venue and meet with the event planner. Have them show you the area where the reception will be as well as any unique locations that can be used to show off the couple. Ask about typical lighting during the reception. Ask about where the band or DJ will likely setup. If it's a daylight reception check if the B&G will have their backs to a bright window during the toasts. (If they do, you are likely to need some fill flash to get decent pictures without completely blowing out the window light). I also like to go the the wedding rehearsal if I can. You often get to see what the lighting will be like, as well as get a feel for the flow of the ceremony. You can check about any rules specific to the venue with the officiant. Possibly look for areas where you could do some bridal couple pictures.

I have owned and used the M5 for about 1.5 year. It is a very capable camera. I have not used the M50, but when I looked at the specs I felt that I would be still be happier with the M5 (which I already owned). The M50 seems a bit of an underachiever to me. I used the exposure compensation dial on the M5 constantly when shooting travel and family pictures. This dial alone may be worth the additional cost of the M5 for me. Absolutely great when you are shooting backlit subjects since the view finder will show the picture with the current compensation level applied. I think the M5 is a more capable camera, but it is more expensive. I do not do video with the M5. The M50 seems to have better video capabilities.

I use a EOS-M to EF adapter when at home, but primarily a Tamron 18-200 M mount when traveling. I find the lens & camera to be a very nice combination. I sometimes take my Tamron 90mm Macro with adapter when I travel. When I gave my old EOS-M to my daughter I bought a $25-30 adapter for her that works as well as the Canon adapter that I have.

I purchased a EOS M5 last year and have used it a number of times on trips and at family gatherings. I like the size and the flexibility the camera offers. I have the Canon EF adapter. It works well with every lens I have for my DSLRs. However, for traveling I have been using a Tamron 18-200 EOS-M mount lens. The lens works well with the M5 in terms of ergonomics and quality. I also travel with the Tamron 90mm macro for close-ups. I have used this lens and camera combination (with the adapter) for unplanned portraits and found it to work quite well for that purpose. I recently acquired a 16-35mm Canon that I am planning to use with the camera as well.

I have not used the M5 for portraits as that has primarily been the realm of my 5D3. I have (for fun) actually shot with the Canon 70-200 f/2.8 on the M5. It works fine, but the balance of the two together is just not right in my hands. I have not found any Canon mount lenses that have not worked with the M5 and the adapter (Canon, Sigma, & Tamron brands).

I also still have the Spiratone and a mount for my Canons. I very seldom use it, buts it's still a monster in terms of length.

I have done some similar events where I print out photos for mounting onto buttons. Tethering generally works well. Canon cameras write to both the USB and the card so if the tether fails in the middle of a transfer (as in, "OOPS I pulled out the cord") you don't loose pictures. It is my understanding that Nilon does not write to the card when tethered. I have had to resort to the card a number of times. In the middle of the craziness of such an event, tethering always seems a bit fragile. My main concern is the printing part. I have had more printer problems than anything else in these situations. If I was asked to do an event that required printing more that around 30 pictures, I would not want to do it without a printer designed for robust fast printing.

The RF-605s actually come with the proper shutter cables if I remember correctly.

I have had great luck with a set of Yongnuo RF-605s with various Canon cameras.

For seniors and kids with a parent, I like to tether to my laptop and do initial RAW image corrections automatically as they come in and I also add directly to a sync'ed collection. I let the parent handle my ipad where they can see the pictures. I also show the parent(s) how to pick the ones they like. At the end we all go thru the picked ones on my laptop and get the initial selection done quickly. This method may not work with every parent. I have also used this method for a client during a business shoot except that the client was in another state, but I sent her a link to the Adobe online gallery. It worked incredibly well for her to call her local contact and make suggestions.

I agree, wireless is still too slow and unreliable to use full time. It is getting better, and if you only sent jpegs, it probably OK. Raw files are still (almost painfully) slow.

I received one as a gift. It's actually fairly well made and works pretty well. Many functions that can be fun to try out. I have been playing with the laser function mainly. I am looking forward to trying lightning shots, but some of the reviews have not been as good for this function. I am going to try the HRD function at some point. You can shoot up to 19 exposures for an HDR. While that could be done manually, it would not be so easily accomplished. Is it worth the $120? Yes, if you can afford it and/or find some fun things to do with it.

Tethering is just like using the standard import, only one picture at a time as the picture is available from the camera. If you set a preset in the tethering dialog, LR applies it after the picture is loaded to the computer. If you don't, LR uses what it gets. If a Raw comes in and your don't set a preset, LR does apply about a sharpening of 25 (like it always does for Raw imports), but that's about it. JPEGs are brought in as the camera shot/processed them.

If I understand your first question correctly, I think you are experiencing Canon's newer menu system where there are multiple screens under each of the main items. Earlier Canon cameras didn't have this same functionality (probably because there were less options at the time). For example there are (off the top of my head without the camera in hand) several screens just for the AF functions of the camera, but only one main menu icon at the top. As far as I know you need to move through each of them every time you move across the menu items. I like to set up the "MyMenu" with those I change often. If I remember correctly the 7DII allows at least two "MyMenu" screens. This limits the amount of movement through the menus to get to the ones I use often. I think Canon designs their menu system so as not to embed menus down several layers deep.

After a quick look at the Altura trigger, I am guessing it will work fine for a SIMPLE off camera setup. You will be limited to manual flash (no eTTL) and will have to make adjustments to output at the flash. Not a bad way to learn about off camera flash (OCF). You will find it limiting if you continue with OCF, however. I would not try to exchange/sell the triggers as they are not too expensive and perhaps a good way to learn.I have some old Yongnou 602 transmitters and receivers that I still find use for occasionally. I would also investigate the master/slave system that may be present already in your camera and pop up flash (if it supports this).

I have found that I don't like using the GPS function due to battery drain. If I need GPS data for a shoot, my work around is to take a cell phone picture with Lightroom Mobile and sync it to Lightroom (Classic) where my photos from my cameras reside. Its then a simple copy of the GPS data from the phone picture to all of the pictures taken at the same location with any of my other cameras. Not perfect, but it works reasonably well, especially for cameras that don't have GPS.