I have an older version of what is now the
Speedo Optimus. What I like about this fin is that it is not too long, so that the flutter kick and dolphin kick are really pretty similar with the fins versus without the fins. My previous experience with other types of fins is that if you get the really long (inexpensive) scuba fins from your local sporting goods or outdoor store, then the kicking motion in no way resembles a real kicking motion. Also, the longer the fins, the more stress on your knee joints.
Some people don't use shorter fins is because the shorter fins don't really make you swim much faster, but they do really provide great resistance while imitating the no-kick motion. The longer fins make you go much faster but don't in any way mimic the proper kick.
See if you can try a couple of different styles at the pool from your lane buddies before you buy one that works for you.
BrokenSpoke