Techflex = very stiff. Best for guys over 200 pounds or large waves
HC= medium flex. Good for all .
Alpha = very light . Good quality and fit . Kinda flexy. Best in waves with less push and dudes under 165. Or Any one who likes softer flex fins
Last year - was surfing with a guy running the Future's AM Twin + trailer combo in Alpha - completely snapped one of the large twin fins off at the base. It was slightly overhead conditions - on a bottom turn. I recently picked up a set of the K2 keel fins in Alpha - incredibly light - haven't had enough time on em to give a worthwhile review - right now i'd say ok in smaller conditions but wonder how well they'd hold up in bigger conditions.
tried a set of accelerators in neo glass and was unimpressed, too flexy and plastic feeling for my tastes. can't see much of a difference between neo glass and alpha, similar cheap materials passed of as semi-premium.