I dove with Doug last week in Maui and I will be purchasing 2 pairs of Morfins (for me and my wife). We will be buying them for two reasons: performance (equal to our current fins) and size (advantage in maneuverability and packing). We currently have Caribe-x fins which work great, though they are closed heel and therefore cannot be used with boots. I didn't think we would need to go the open heel route, wish I had known better at the beginning. The Caribe-x's are the only dive fin that I ahve used, so I cannot compare the Morfins to anything else.
Anyway, we tried the Morfins while diving with Doug, then went back to our own fins fo 2 dives. In my opinion, the Morfins work as well as our Caribe-X fins. The Morfins worked best for me with a longer, slower kick. They can really get you moving with a log powerful kick. I found that they didn't work all that well with short, fast kicks.
The second reason I (well, my wife likes them too, but I'm writing this post) like them is that I believe that they have advantages due to their size. Since they are shorter than usual, they are more maneuverable. Also, they have less of a side-profile so they seem to slip sideways through the water more easily. This was helpful when exploring small caves and when maneuvering to capture critters on my camera. The size also comes into play in that they will pack more easily than our longer fins.
Overall, I would not say that they are dramatically better than our current fins in terms of how fast they can go, however dive fin performance shouldn't be based solely on speed. Maneuverability is very important as well and the size sealed the deal for us as we dive while on vacation and smaller fins are easier to pack.