Out of Air Method

[LKunze]

DIR divers tend to have their buoyancy skills in check and should not have an issue with drifting far away from their buddy causing the reg to be ripped out of their mouth by running out of hose.  For new divers that have undeveloped diving skills or divers with poor diving skills, the grab onto your buddy thing is probably best.  In either case though donating the primary regulator on a long hose and switching to the bungee backup regulator is still the easiest and best way to go in my opinion rather than fumbling for an octo mounted somewhere on your BC. 
Personally, I have a real problem with this method.  The last thing I want to be doing or my buddy doing is screwing around with each others gear...particularly the inflator hose.  This is completely unnecessary and has the potential for creating a CF situation real fast.  The only reason a diver shouldn't be able to control their own buoyancy on ascent sharing air is if one of the divers becomes incapacitated at which point you are not really sharing air but trying to get your buddy to the surface as fast as you safely can or if your buddy has a BC failure due to a tear or puncture.