[Mullins]

Yeah I'd always go for the softer option where there's a choice as I really don't find soft fins lack power off the bottom. However that's just me, there are guys out there who use 40s for reasons I can't fathom. The DiveRs are good fins and you probably wouldn't pick up any genuine benefit from moving to C4s, but they might feel snappier due to their length. The DiveRs are very long, so if you're doing bicycle kicks with them you'll find they'll fold and the tips won't provide much thrust. Those long fins really require wide, straight-legged kicks. Easier to do this in the sea than in the pool.

You do need to bend your legs a little when bifinning, but the quads are really only working to transfer power from the hip flexors. If you look like you're riding a bicycle then you're bending them too much. There are a few good bifinning videos around, one that I can think of is Will Trubridge's 88m in last year's triple depth. Maybe a video of that event is on Trux's website? Or youtube.