My understanding, and it's from probably a decade ago, is that the wedge type pull the holder down as they tighten so the height is repeatable assuming the lock nuts are tight.
The piston ones lock but I think you have to apply downward pressure on the holder while you are tightening. More of a two handed operation.
The piston ones lock but I think you have to apply downward pressure on the holder while you are tightening. More of a two handed operation.