I just got back from a trip to Little Cayman using Mares Avanti Superchannel full foot fins for the first time. We bought them to replace Atomic Open Heel Split fins due to weight and size considerations for luggage. For starters, they were much lighter than the Atomics and much smaller to pack, especially when you consider that you don't need booties either. I really liked the Atomics and always felt fast in them, but I have to say I felt like the Avanti Superchannels might actually accelerate faster and have a comparable top speed. What I really liked was that the Superchannels were much easier to frog kick and to scull backwards in. I felt much more maneuverable in them.
I went down there a little hesitant about using a full foot fin, and came back a believer. If I am diving colder water, shore diving, or in rougher water, I still want the booties and open heel fins. But in warm relatively calm water boat diving, the full foot fin was definitely the way to go and my wife and I were both very happy with the Avanti Superchannels.