I too prefer upstream models; and I haven't managed to get any of mine to free-flow either. With the exception of the downstream Cyklon, all of the Poseidon regulators are of that ilk -- either with over-pressure valves in the hoses, in the case of the older models; or, now, most commonly, on the first stages.
To be sure, any regulator is capable of free-flowing under inclement conditions; but it seems more of an issue of user error; not handling the gear well; huffing on the regulators; not keeping them as warm as possible, before water entry, than an issue of any particular brand . . .
