I am unsure about other manufacturers and will respond to what I know. The ball on Ultralight parts minus the o-ring is 0.962 or 24.44mm. The ball on the Nauticam buoyancy arms I have is 0.968 or 24.57mm. I have a side business where I run dive charters and see plenty of rigs with mismatched accessories. I never hear many complaints, and the ones I do hear about usually are always resolved with maintenance and/or new o-rings. The only problem I see at times is if you have two different manufacturer parts on each end of a clamp, like an Ultralight arm and a Nautivam arm both using the same clamp. This will cause the clamp to clamp down slightly at an angle, which creates problems with tightening and loosening.
If you have parts that are the same on both sides, they clamp the same. I haven't inspected other manufacturers clamps enough to see how the area is where the ball sits but I would assume there is a very slight difference. This could create problems but I wouldn't think it would be noticeable.
Now, whether you should use fine or coarse-threaded clamps is up to the user and what they believe or have used previously. Here is a blog I wrote on this very subject-https://ulcs.com/2023/11/14/which-type-of-clamps-coarse-or-fine-threaded-are-best/
One thing I know for sure is when something isn't holding (after all maintenance has been done), it isn't necessarily the parts. I have done several unscientific tests with our parts and can get a combination of Ultralight arms and clamps to hold 5 lbs overnight at 24" horizontal out from a fixture like a vise. The problem is most people cannot twist the knob tight enough to make this happen. I used a special tool I made to test and prove this, and this was done with all course threaded clamps. Personally, I don't use our fine-threaded clamps on my own rigs. Our AC-CSB coarse threaded clamp seems to work really well when something needs to be tight, and the person using them has the strength in their hands to tighten them enough. Just last week I had someone come by the shop with their DSL camera with the complaint the arms always moved letting the strobes spread out. We switched the arms and clamps to all Ultralight using the CSB clamps, and no matter what angle they moved the camera to and no matter how hard they shook the rig, the arms and clamps stayed put.
Sorry for the lengthy reply, but I believe that by providing as much information as possible, you can all make a better assessment of what you might need for your camera rigs.