that plastic fins suck. anyone who claims not to be able to tell the difference between a good, high quality fiberglass fin & a crappy stock plastic fin is questionable as a surfer, IMO.
you pay more for quality. the industry has everyone convinced that stock plastic fins are acceptable b/c they're light, but there's a trade-off (ie: loss) in performance. plastic fins are too soft, they flex too much/easily & don't return that flex back to the board in the form of energy or drive like a fiberglass fin does.
wow, after all these years, i'm questionable as a surfer. perhaps i should re-evaluate my existence all together?
but so be it. i can tell you for certain that, in the short time i've had these (albeit on some chest-high surf, at best), i don't see a significant difference between these and the FCS fins they replaced. sorry to sideswipe your whole fin gig, but it is what it is.
perhaps when it's overhead and barrelling, as mentioned above, i'll realize the gravity of my error. of course, here on the East Coast, it might be a while before that happens.