Do check out the link imagemeister provided above. It shows you the different types of gimbals available.
I use two tripods with gimbal setups...
One I've used for around 5 years is an inexpensive "J-type/bottom mount" that's a Chinese copy of the original Wimberley WH-200 (
https://www.tripodhead.com/products/wimberley-main.cfm). This is what I call a "full size" gimbal because it fully replaces any other tripod head making it "large lens only" (unless you remove the head and switch it with a "standard" tripod head of some sort). This type of head ranges in price from around $100 to $500 or more. They can support a relatively hefty camera and lens (10+ lb.), are fairly large and the metal ones typically weight around 3.5 lb. You can shave roughly 1 lb. weight buying a carbon fiber, but the price will be higher. (Beware of "fake" carbon fiber that are merely metal wrapped with CF to look the part... also be wary of "no name" manufacturers since carbon fiber is tricky to work with.) J-Type/bottom mount gimbals are among the most adjustable, so can accommodate a wide range of lens sizes. There are also J-type/side mount variants, which typically recommend use with slightly less heavy gear (perhaps up to 8 or 9 lb. lenses). There are also some gimbals that are convertible from side to bottom mount, though it may be necessary to buy separately sold accessories.
The other gimbal I've used a lot for 20 years is a Wimberley Sidekick SK-100 (
https://www.tripodhead.com/products/sidekick-main.cfm). This is a "gimbal adapter" that's used in conjunction with a medium to heavy duty ball head (I use a Kirk BH-1, rated for 50 lb.). The Sidekick side-mounts to a lens, providing the tilt axis movement. The panning axis is done by the ball head itself. To work with a gimbal adapter, the ball head must have an Arca-Swiss quick release platform as well as a separate panning axis. There are several brands of these now, ranging in price from around $100 to $250 for the Sidekick. Induro makes a close copy of the Sidekick for around $200. Jobu makes a "Mini" that's about $110, but is only usable with smaller, lighter lenses (such as 70-200mm, 300mm f/4, 400mm f/5.6, 100-400mm). To use the Jobu with some lenses requires a spacer, which Jobu sells as a separate accessory. There are also some Chinese knock-offs of the Sidekick now, selling for around $125.
One of the biggest advantages of a gimbal adapter is that the tripod can quickly and easily be reconfigured to use without the gimbal... i.e., with smaller, collarless lenses on your camera. There's no need to swap heads, like there is with the full size gimbal discussed above. While the Sidekick is recommended for up to 8 lb. lenses and have personally used it with 500mm f/4, I've seen people use them with heavier (such as 400mm f/2.8 and 600mm f/4) without any problem. The Sidekick itself weighs about 2 lb., while a heavy duty ballhead typically weighs a little over 1 lb. So the combination ends up weighing about the same as a metal, full size gimbal. But the Sidekick and ballhead are considerably less weight than carrying both a full size gimbal and some sort of standard head to swap out with it, plus any tools that might be needed to do that swap. (No tools needed with the Sidekick.)
All gimbals require a lens with tripod mounting ring and some sort of Arca-Swiss quick release compatibility. A few lenses have an A-S dovetail built in, notable several recent Tamron telephotos. But most require a lens plate, or a replacement tripod mounting foot, or even a replacement tripod mounting ring. This is an additional cost to use a gimbal. They sometimes come with a "generic" lens plate, but a better one with some sort of "anti-twist" feature might be recommended. Figure $25 to $40 for a quality lens plate. A replacement tripod mounting foot is lens-specific and costs $75 to $150. If necessary, a full replacement tripod ring will be lens-specific and typically cost upward of $200.
The Manfrotto U-shaped gimbal Gene shows is one of the lower cost options and somewhat unique. Out of the box it comes with and uses a proprietary lens plate (extras are available if needed for add'l lenses). But it also can be modified pretty easily to use more common and widely available Arca-style lens plates. The Manfrotto 393 and one or two other similar gimbals are able to handle heavy lenses at a lower cost, but are themselves among the heftiest gimbal heads.
The Arca-Swiss plate (or Manfrotto's plate) are a little longer than the lens' tripod mounting foot, to allow the camera/lens/accessory rig to be slid slightly forward and backward for equilibrium. This is the "secret" of gimbals. When set up properly, they allow big heavy lenses to be used smoothly and easily with a very light touch. Lenses that are IF and IZ (internal focusing and/or zooming), that don't change length and remain balanced will work best. Lenses that change length (non-IF and/or non-IZ) will often be a little out of perfect balance, as the barrel extends and the lens changes length. One of my lenses (100-400mm) is this type, but I only find it a minor inconvenience. The main thing to remember with a lens of this type is that the tilt axis needs to be tightened and locked when you aren't holding the camera or lens, because if it's left loose the change in equilibrium can cause the rig to tip forward or backward.
I use my gimbals most often with 100-400mm (~4 lb.), 300mm f/2.8 (~ 6 lb.) and 500mm f/4 (~ 8 lb.) lenses. Typically those lenses are fitted to a camera weighing about 2 lb. (w/grip and batteries), and sometimes also a teleconverter (~ 1/2 to 3/4 lb.), a flash (~ 1 lb to 1.5 lb.) and flash bracket (< 1 lb.). No problem with either gimbal supporting even the heaviest of these combinations.
I don't use either gimbal often with 300mm f/4 (~ 3 lb.) or 70-200mm (~ 2.5 to 3 lb.) To me these lenses seem too small and light to balance very well on a gimbal. (I have not tried the Jobu "Mini", which might be more appropriate). But, to be fair, I bought these lenses primarily for hand held or monopod use anyway... i se them when I need to be as mobile as possible.