Do they provide better performance?
Yes . They make the lift much more sturdy.
It doesnât really matter either way, just whichever you prefer.
If you are going to be using metal shaft collars I would suggest replacing the small inlet(or whatever that black things name is) with a screw. If you use starscrews you can use a torx driver to really tighten the metal shaft collar onto the axle making the shaft collar stay on the axle for the entire season without worry about loosening. 
Using them to brace various things with standoffs, you have to use a coupler, but if you are using them on shafts you are correct that it is best to use a .25" screw rather than the setscrews.