Sorry, you're wrong. Firstly, I'm agreeing with all your comments about twindies. Main issue is practising and following the protocols to switch regs to balance gas usage. The *standard* twinset longhose primary donate works exceedingly well and absolutely excels when deco gasses are involved. The donate is whichever reg you're breathing from: no thinking, just grab the reg in your mouth, duck your head and donate, then scoop up the necklaced backup just under your chin. It's a completely automatic procedure taking less than a second. It's so effective that all agencies accept this as *the* standard configuration for diving with twinsets, and pretty much mandate it for technical diving with twinsets. Sorry, that's all agencies except BSAC.