I use these on all of my tools. Many are near a thousand pounds (if not more) and I have no doubt they can handle the weight well. The wheels on the heavier-duty bases are steel and not coated with rubber or PVC. The casters on all sizes feel well suited for the weight load. When the base is locked down, the machines feel sturdy and do not feel like they will roll away on you. They are low profile, but will raise the machine up about 5/8 of an inch. The base has a square of sheet metal at each corner for the legs of the machine to rest on. It measures about 4 1/2 inches square, so plan accordingly. Grizzly's recommendations as to which base fits which machine has been perfect. The finish is tough and overall I've been happy.
Here are some flaws:
The assembly is annoying because it requires lock nuts to be inserted backwards... meaning you need to thread the lock nuts vinyl-side first. This will likely result in cross threading. To make it work, you should thread the nut on a bolt the normal way so that it can cut the threads through the nylon. Then remove the lock nut, reverse it, and carefully rethread it nylon-side first. This is pretty time-consuming.
the tool does get recessed into the base. I've had an issue with a low door on one machine, and a "Grizzly Extreme Edition" plate positioned so low as to interfere with the recess. The solutions were simple, but buyers should be careful about it. The recess is about 2 inches, but the bolts extend above that and can interfere with low doors. I had to remove the Grizzly vanity plate on one tool, and shorten two bolts on a base for another tool. All of my other machines fit well.
When locking up the base, you thread an undersized plastic knob until the magnetic foot hits the floor. When lifting the foot, if you thread it up too far, it'll drop the foot back down. When fully lowered, the rubberized foot sticks to the floor when left supporting the weight for even short periods of time (my floor is unfinished concrete, so it's not any type of floor coating that is responsible). I've had to physically pry them up sometimes. Not a big deal, but a nuisance.
The worst thing about these bases is the clearance. One would think that lifting the machine 5/8's of an inch would give you that much clearance. However, you only have about 1/8 of an inch in clearance because the feet can only be lifted that high. I've included a picture for reference.
Despite these disadvantages, the overall quality is very good and they do feel solid and are priced well. I am glad that I have the range of bases available to move up to 1,000 pound machines around my small shop on a daily basis.