I think a good number of people use them but me personally would not like them because I like to shoot at the same spot to see a group. I haven't yet gotten a robin hood but I shoot some tight groups sometimes and I know if I would be shooting FOB's I would be ruining them. I think they [FOBS] are supposed to come off the arrow when you shoot at an animal so that they "mark the spot of impact".
FOBs are pretty cool. The biggest issue when switching to FOBs is having the proper clearance around your rest. Some folks have issues trying to get them to clear the rest. They buck the wind better than most traditional fletching and are just another way to steer the arrow. Since the FOB is held in place by your nock when you get a pass thru the fob and nock pop off the arrow as it goes through the hide. Which some see as marking the spot of the shot and others view it as a chance to loose a fob and nock.
i was gong to switch to shooting easton gold tips this year. But the more feedback I get about the fob I am prob going to just stick to my blazers. I want to shoot lumenoks and I dont want them to pop off the arrow and vanish into the ground. They do sound very cool. Thanks for all your feedback and help guys!