Hey IceAxe,
I too asked this question a couple of years ago. I noticed that some of the DMs on some of the boats that I was diving from were diving with FF fins. I decided tha I liked the idea about not having to deal with my boots for warm-water dives.
I begin to see reports in Scuba Diving about FF fins being more efficient than MOST of the open-heeled type. Sooooo, I decided to buy a second (or was it my fourth set? ha!) pair of fins in the FF variety Just to see if they were any better.
Not wanting to put very much money into this experiment, I bought the cheapest FF fin I could find at LeisurePro.... the Oceanic Carribe. They were $19.95.
These cheap fins were a big improvement over my larger, heavier, open-heeled Tusa Imprex fins. They are faster. It SEEMS to take less effort to move myself around. Because they're so much lighter, traveling with them is great. These particular FF fins are a bit too soft for diving...so, I'm now looking for a little stiffer fin to replace these.
The downside is that any FF fin is only for warm-water diving. Shore diving with FF fins means that you're probably going to have to wear some type of flexible water shoe into the water, stow the water shoes in a BC pocket, and then put on the FF fins. Complicated.
However, I will glady deal with that complication to realize the benifits I mentioned when warm-water diving. If you can find the old Scuba Lab reports from a few years back, I believe that they will back up my statement about being more efficient and generally faster than the open-heeled fins.