I dove with Fish & Fins last week. I will echo the "Cater to European" comment. Only one other diver was American during the 4 days I dove with them. My only complaint would be that the most of the divers on the boat I was on only wanted to do 2 dives so it was always back to the shop before the 3rd dive. We did do 2 wrecks and short drop off for the third dives so they weren't bad dives, just not out at Blue Corner, Ulong Channel or the outer reef. This also happened with Sam's Tours on one of the 2 days I dove with them 5 years agoi. The staff at Fish N Fins was professional and very competent. The guides were considerate of where the divers on the boat wanted to go and went to Ulong Channel & Shark City based on the desires of a group that were leaving the next day. (Great Dives, but Palau and Great dives are redundant!) 5 years ago there were more Americans diving with Sams Tours on the days I was there. I do not know if this is still the case or not. There appear to be a large increase in the Japanese Tour market and Fish N Fins used a separeate boat and guides for a large group of Japanese.
I do not think you will find any problems diving with Fish & Fins unless you do not want to be with a number of French, Germans and English divers. But that's what travelling abroad is about, meeting divers from other countries and cultures. Most of the european divers on my boats did speak English so communication was not a problem.