The swivel parts would seem to better sit flush with any slopes on the floor and having the hex shaft would make adjusting easier (fingers, wrench, pliers). I'd probably go for threaded couplers too as opposed to the T-nuts. As long as possible to minimize any slop and rocking. I'd think you could adjust these easily enough with just fingers since having to break out a wrench could get old. Just a drill hole with the OD and depth of the coupler, then a clearance pilot for the shaft size of the foot threads. Goal is minimize side to side wobble of the table and easy adjusting. This is what you see on many mobile bases except they usually just have a diagonal plate at the corners and have nuts top/bottom to tighten up the feet.
