I understand the wish to be able to move the system around. When I built the frame for my FineLine system, I tried to use a knockoff version of these, and was not impressed. They were very wobbly when the machine was on the leveling feet. There are a few problems with them:
1) The feet are coated in rubber, so they tend to flex. This is probably the smallest issue.
2) The feet don't spin with the adjustment thread. Instead, the threaded rod rotates with the adjuster wheel or lever. The threaded rod has to bear weight on the main casting, but it still has to spin, so they end up screwing a very small screw into the end of the threaded rod. The end of the threaded rod sits on a bearing with only the weight of the machine as pre-load (maybe 150-200 lbs in your case). This means that there is very little to keep the threaded rod from flexing at that joint.
As I said, I tried a knock-off version, so the Footmaster version might be a little better. Either way, the bearing that supports the caster relies on the weight of the machine for preload, so it will never be as stiff as a leveling foot. With standard leveling feet, you can add a lock nut and put some real preload on the thread (Easily 12000 lbs on a 1/2" thread if not way more) which helps make it stiffer. Something like this would work better with regular leveling feet:
Workbench Locking Caster Kit (4 Pack) - Rockler Woodworking Tools
Unfortunately, these are not really rated for the weight of a 48x96 CNC machine. If you aren't going to move it too often, you could use standard leveling feet and mount standard casters off the sides of the legs. When you need to move it, lower the machine onto the casters, then re-level the machine in the new location. You probably will have to re-level the machine anyway, unless you are lucky enough to have a really nice floor.
Ultimately, I decided to just use leveling feet alone. If I need to move the system, I will use a floor jack to jack it up and put it on either moving dollies or dolly casters like this:
https://www.tractorsupply.com/tsc/pr...aster-6-in-dia
-Robert