I tried them all. I think they all work on the same principle. My observations:
Manfrotto hydrostatic arms: they don't feel as precise as the others, and the knobs are smaller
Foba: the best, but also the most expensive ones. very clever clamp/hook. there is a version with progressive tightening, but they are at around 400€ each.
Fisso: handle as nicely as the Fobas, but are quite cheaper, especially if you buy the set. one drawback is that their treads are not like the tripod threads, so monting a camera is out, but I don't do that anyway
I keep on buying more and more of these. Nowadays I can't imagine working with anything of lesser precision. whatever you need to fix, they hold it. They are very sloppy when untightened, so you can adjust easily. tighten the knob and there is no more movement. sweet! for heavier stuff i use the magic arm.