sorry for being so anti poseidon but with so many excellent "modern design" regulators on the market i cannot believe why anyone these days would want to buy such a dated totally w--k bit of gear.
i've dived with every model including the new one from various divers and they all breath like a bag of shite .
cant vouch for the ones youve tried but if there properly set up (easy to do yourself) they are a real good reg, ive got cyclon, jetstream and Xstream and they all give a nice breath (cyclon is poss the nicest at shallower depths) for me one of the best things was the simple tried & tested Bomb proofness of them, - unlike my previous Scubaflow reg which had a habit of freeflowing the posiden regs have never missed a beat.yes they diliver the air in a differant way to most modern regs but thats not to say it's a bad thing - its like Doctor Pepper's - youve gotta try it to love it!!!
duncan must have had the out of the box untuned versions .
they all seemed to me to have a breathing rate designed by a swedish porn star on the vinegar stroke ,a sort of nothing followed by a frantic whoosh coupled with an over sized mouth piece designed for the mouth of fozzie bear i can't say i could live with one.
everyone to there own
all the best elfyn