So this one will take some explanation, because I will talk about the dreaded split fins.
As an instructor teaching pool classes, I used the same rental gear we had the students use. One day on impulse I put on a pair of ScubaPro split fins--don't know the model name, but they were soft--downright floppy, IMO. When I tried to cover distance going forward, I felt like I only had booties on because I could not feel the movement of the fins at all. Yet, I was indeed moving forward, albeit not at a pace I liked. I back fin a lot when working with students, and I absolutely could not do that with those fins. I switched out to the usual blade fins before long.
A few years later I did a refresher class with a father and his teenage son, and this was done in a recreation center pool with no easy access to rental equipment. The father and son had all their own gear, and I had mine. They each produced a pair of Atomic Split fins, but I saw immediately that there was a mistake. The boy was a below average size for an adult, but he had a pair of size Extra Huge fins. He insisted they were his, but we eventually decided that he must have accidentally swapped with someone else after his last dive, because putting his feet in those fins was like walking into a room. I gave him my pair of Cressi Frogs mentioned above, which were still too big for him, and I wore his Atomic splits, even though they were so big on me that the spring strap barely touched my heel. The fins did, predictably, come off on occasion, but I had surprising success otherwise. I could even backfin shockingly well, although I could not use my normal technique because of their lack of a wide sidewall. The difference was that the Atomics were much, much stiffer than the ones I tried before.
In summary, I decided that drawing judgment on split fins, you can't be too generic. Perhaps the weak, floppy split fins I used the first time would be just fine for a weak-legged individual who is only going to go in a forward direction with a flutter kick, meaning most people would hate them. On the other hand, the big, stiff split fins would work well for most others, although I would still prefer plain blade fins with wide sidewalls for the kind of diving I do.