IMO most of them are alright (for example, the metal materials completely destroy your speed in exchange for the extra power), but the feather ones have incredibly high speed and strength, with no downside other than the lack of natural healing (which isn't really that detrimental, since with Phoenix Feather/GEF limbs you'll almost never get hit anyways).
I once loaded up an old save that was on GC4, decided to change all my limbs to ommel hair and just sprint downward and see how long I'd last. I ended up killing Elpuri and getting the freedom ending, with a very low score of around 80k. My armor was crappy, and I was wielding two +5 hand axes made of weak materials (iron or steel, I think). No victory should be that easy in IVAN.