I've gone through 3 or 4 pairs before getting any that don't hurt or give me foot cramp after 20yards.
(Wide foot across the ball of the foot)
I ended up with finis floating fins. Quite long. But the foot pocket was the softest I've tried so more comfy.
I use them for alignment drills (side kicking, Unco drill etc) more than for pure 'improve kicking per se' .
Swim Smooth info points at fins being THE most useful tool for training.