I've nothing but good things to say about these. They're incredibly comfortable (I'm used to monofins which crush your feet haha), I can wear them for our entire 60 minute training sessions without any pain whatsoever. Good power transfer for bifins. They're perhaps a little on the softer side, my medium stiffness feels very flexible, but then again, my only reference is monofins. For reference, my shoe size is 38/39 EU, I ordered these in 39 and they fit like a glove with my 2.5 mm socks.