These ball heads seem to be extremely good value and appear to be nicely finished. Their relatively low price causes me to suspect that they may be missing something in the way of performance or durability. I would appreciate input .
When I bought my Feisol tripod 4+ years ago, the place I purchased it from had a ballhead there. I was not impressed with the quality at all. The movements were not smooth and it didn't seem to lock down well. Also, even though the QR system was designed to function similar to ACRA standard, a bit of research showed that was not really close in dimensions, so I passed on it. Also, the tape on CF look was really cheesey to me. Remember, this was 4+ years ago when I looked at one. Nowadays, I have no idea how good they are. FWIW, I have a RRS BH40 and plates.
In the 4+ years of decent use on my tripod, I have had no problems with it and I REALLY like it. Based on pictures and the few reviews I have seen, their tripods seem to have gotten much better in quality since I bought mine. I would assume that their ballheads may have gotten better too.
Have you considered PhotoClam? Nothing but rave reviews for them. I remember reading at least one review where someone replaced their Feisol head with a PC and were pleased with the difference.