Well I decided to try the mono fin thing out.
I got a Waterway Model 2 Long Distance


This is with the re-enforced heel (the tan bits of rubber), the edge protectors (those black stripes on the side) and the neoprene inserts to reduce blistering (the black stuff inside the fin).
It is a fun fin, the only other mono's I have tried are cheap little plastic toys and a Waterway Model 1 - Hard. The Model 1 hard was too hard for me and it was tricky to prevent it from slipping side to side. It felt like there was a big thing at the end of my feet.
What is fun about this fin (Model 2, LD) is that it dissapears. Sure when I fisrt started swimming I got some of the slip, but once you start moving, it barely seems like it is there. When surface swimming there are no splashes, I just shoot along. When being silly and coming up from 5m I can shoot myself up to the middle of my thighs out of the water.
At the moment the up-kick feels kind of weak to me. I am an experienced dolphin kick swimmer (back before I was fat and old I used to race butterfly) and it is definetly a different timing. Also I find it is easy to slip into poor form because you still have power! You can just wiggle you ankles and go somewhere with the mono. I like to use this fin for a full body dolphin kick.
It is a fun fin, it does feel like it extends you whole body and shoot it through the water in a way that dolphin kick with bi-fins does not do.
When really trying hard to power this fin I could cramp my feet and calves, but it is possible to stretch them out in the fin.
This fin I suspect is too soft for me to really send me deeper, but perhaps not it is a really relaxing fin (though my times for 22m and 44m were the same as with my Cressi Gara 2000 HFs)
On Fit
Foot pockets:
the 310 aka 45 are the larges foot pockets Waterway makes. I have large feet. They are only 43 long, but EEEE wide, and they are tall. It turns out with this foot pocket style "tall" is the most important factor. There is plent of width, there is plent of length, but barely enough hight (your foot goes much deeper inside than with tradional fin pockets)
I should not have ordered the neoprene padding, as it reduces the room inside the pocket.
Putting these fins on pinches a nerve on the top of my right foot that send pain down through my toe
Once my foot is in the pocket seals arround the foot, making it difficult to slide my foot deeper inside, but it only resembles comfortable if I slide my foot deeper inside. I could not even wear lycra socks in these as they stand. I am hoping there will be a little bit of rubber fatigue and wear of the neoprene to make putting them on easier. The left foot (a few mm smaller) is pretty decent.
So far 15 minutes was the longest period of time that I was able to wear them before needing to take them. They really do seal, there is no water exchange and they make my feet warm!

Ordering Mistakes:
Of course it would have been better to try on the footpockets ahead of time, but I had tried a pair of 43s and they were not too narrow, but were tight so I though just up the size and I would be OK. They are suppose to fit tight. I should not have gotten the inserts, I should have planned on using a neoprene or lycra sock.
I should not have used Polyorg. I had seen a couple of responses of them being slow. 4-6 weeks menat a little over 4 months, the other swim goggles in my order did not arrive. Just not responsiveness from the owner. It was frustrating. Though in the end I did get a nice fin and a mono-backpack.
I should have not entered 200-400m swimming distance (while that is realistic) I am not racing those distances and I should probably have gotten medium stiffness fin (I did ask for a medium stiffness fin, but I checkind the box for longer distance)
I probably should have gotten a fin with Omer footpockets. I think the comfort would have made them more fun and easier to let other people try.
I got a Waterway Model 2 Long Distance


This is with the re-enforced heel (the tan bits of rubber), the edge protectors (those black stripes on the side) and the neoprene inserts to reduce blistering (the black stuff inside the fin).
It is a fun fin, the only other mono's I have tried are cheap little plastic toys and a Waterway Model 1 - Hard. The Model 1 hard was too hard for me and it was tricky to prevent it from slipping side to side. It felt like there was a big thing at the end of my feet.
What is fun about this fin (Model 2, LD) is that it dissapears. Sure when I fisrt started swimming I got some of the slip, but once you start moving, it barely seems like it is there. When surface swimming there are no splashes, I just shoot along. When being silly and coming up from 5m I can shoot myself up to the middle of my thighs out of the water.
At the moment the up-kick feels kind of weak to me. I am an experienced dolphin kick swimmer (back before I was fat and old I used to race butterfly) and it is definetly a different timing. Also I find it is easy to slip into poor form because you still have power! You can just wiggle you ankles and go somewhere with the mono. I like to use this fin for a full body dolphin kick.
It is a fun fin, it does feel like it extends you whole body and shoot it through the water in a way that dolphin kick with bi-fins does not do.
When really trying hard to power this fin I could cramp my feet and calves, but it is possible to stretch them out in the fin.
This fin I suspect is too soft for me to really send me deeper, but perhaps not it is a really relaxing fin (though my times for 22m and 44m were the same as with my Cressi Gara 2000 HFs)
On Fit
Foot pockets:
the 310 aka 45 are the larges foot pockets Waterway makes. I have large feet. They are only 43 long, but EEEE wide, and they are tall. It turns out with this foot pocket style "tall" is the most important factor. There is plent of width, there is plent of length, but barely enough hight (your foot goes much deeper inside than with tradional fin pockets)
I should not have ordered the neoprene padding, as it reduces the room inside the pocket.
Putting these fins on pinches a nerve on the top of my right foot that send pain down through my toe
So far 15 minutes was the longest period of time that I was able to wear them before needing to take them. They really do seal, there is no water exchange and they make my feet warm!

Ordering Mistakes:
Of course it would have been better to try on the footpockets ahead of time, but I had tried a pair of 43s and they were not too narrow, but were tight so I though just up the size and I would be OK. They are suppose to fit tight. I should not have gotten the inserts, I should have planned on using a neoprene or lycra sock.
I should not have used Polyorg. I had seen a couple of responses of them being slow. 4-6 weeks menat a little over 4 months, the other swim goggles in my order did not arrive. Just not responsiveness from the owner. It was frustrating. Though in the end I did get a nice fin and a mono-backpack.
I should have not entered 200-400m swimming distance (while that is realistic) I am not racing those distances and I should probably have gotten medium stiffness fin (I did ask for a medium stiffness fin, but I checkind the box for longer distance)
I probably should have gotten a fin with Omer footpockets. I think the comfort would have made them more fun and easier to let other people try.