"Monkey Diving" does not = no BC in all cases. If you are in warm water with no exposure suit, and a buoyant tank why what purpose does a BC serve?
If you have an exposure suit and larger cylinder some sort of BC would be prudent.
The "Monkey Rig" does not preclude the use of a canister light.
The "Monkey Rig" does not preclude team diving. Keeping the team in contact is more challenging with a scooter, but that's true with a BP&W also.
The "Monkey Rig" does not preclude the donation from the mouth, and allows a bungeed backup, both in compliance with DIR guidelines.
The "Monkey Rig" does not preclude using larger cylinders. A "side mounted" AL80 is very streamlined, and in compliance with DIR guidelines regarding stages. Do "DIR" divers routinely scooter while breathing from a slung 80?
We have prototyped a "Monkey Diving" BC that offers 8 lbs of lift, and closely mimics a Hogarthian harness. This enough lift for modest exposure suits. A 3 mm wetsuit and slung Al 80 with a few lbs of lead is a "balanced" rig.
How does this differ from a "DIR" compliant BP&W?
No backplate, the 80's is slung, and the harness has some sewn components.
Would I recommend this configuration for inexperienced divers? No, but I would not recommend a scooter for newbies either.
Would I consider it for any type of overhead? No, but there's no single rig I would take in an overhead. Monkey diving should be limited to shallow depths and good conditions IMO.
Is it possible to use a "Monkey Rig" in a unsafe manner, i.e. solo, overweighted, without a dive plan or insufficent training or support for the conditions? Sure, but that's true for a backplate and wing also.
Keep in mind my comments are specifically about the rig we have developed, i.e. small BC and slung AL80.
Monkey diving is not DIR, no doubt, and I'll not argue that it is, but many of the same principles can be applied.
Within the limits I've stated, a unified team, sufficent gas for the conditions, back up regs and long hose (5 ft) primaries, canister lights for communication, a balanced rig, with sufficent lift for the job, adequate training and adequate support (chase boat) what are the specific problems that you see?
Tobin