The first, and perhaps most important, reason why recreational scuba divers have not been able to use conventional monofins for scuba diving is that the fin loads pitch the swimmer's body up and down as the fin is stroked which results in the user's head getting repeatedly knocked on the back of the head by the tank valve as they swim. This reason alone takes conventional monofins out of the running for scuba fins in recreational diving applications. The underwater orienteering configuration avoids this problem by moving the scuba tank off the divers back, making it a hand-held system instead. It is a very effective solution for them, but not a viable solution for recreational diving.
The second reason is that, even if you solve the pitching problem when applied to a scuba diver, the traditional monofin will not be that much more efficient than the scuba fins they had been using. The details of why this happens gets rather complicated, but the truth is that the classic monofin will not experience the same efficient operation on a scuba diver that it can provide to a freediver. The primary reason for this is the same reason why monofin technique is so important for freediving and fin-swimming performance, but there is also a secondary reason with the fin's Strouhal number drastically falling off design point.
The DOL-Fin HP solves these problems and spikes the thrust efficiency for scuba diving so drastically that it will be difficult for scuba divers to comprehend the importance.
There is the safety element. The ability to swim fast does not mean that you have to swim fast, but it means that you can when you need to. Every year there are many diver emergencies, resulting from divers being swept away by currents and unable too get back to their dive boat, sometimes with drastic and even fatal consequences. Also, the reduced work load the fin places on the divers body will reduce the effects of narcosis at depth and will also reduce the divers susceptibility to DCS in relation to the decompression models in their dive computers.
The DOL-Fin HP's swimming efficiency also can significantly extend dive times.
Many divers are transitioning to rebreathers, and units like the KISS GEM (Gas Extension Module) are being introduced to serve the recreational market as a way to extend the duration of standard open-circuit (OC) scuba. Although much as been done to eliminate the operational complexity and improve component reliability in the KISS GEM, it still retains many of the risks that rebreather divers are exposed to over and above OC scuba divers.
In contrast, a DOL-Fin HP can extend the standard OC scuba by lowering workload instead of recycling breathing gas. In doing so, it not only avoids the risks associated with gas recycling, but it introduces the fore-mentioned safety elements to the dive as well. Plus, the lower workload can produce a more relaxed and enjoyable dive, and that is very important in recreational diving.
All these elements combined are very significant in my opinion, but most divers will have a hard time comprehending this and how it can benefit them. They will look at the DOL-Fin and only see a speed machine. They will likely think "I don't swim fast when I dive; I don't need that weird looking thing" and they will walk away. It will take time and education for them to begin to understand the benefits, which is why I said that the DOL-Fin HP is probably years ahead of its time (at least for scuba applications). If freedivers help to spread the word on these benefits, it might help to shorten the time lag which may ultimately benefit freedivers too. The scuba market is presently much larger than the freediving market and can be a base for manufacturing volume that can drastically drive down costs and add diversity to the product offerings as well.