I've seen both used. Not sure which exact model of a Halcyon b/w you're asking about (or even if there are multiple) but Halcyon b/w rigs (and weight belts) are the university standard for the uni I'm working with in Maine and I know divers I work with in Oregon who use Hydros Pro. The Hydro has more hardware and more features to get used to, biggest I know of being the integrated weights. The Halcyons here are very simple, minimalist b/w rigs and as long as the straps are sized properly to you, won't give you any issues. If you like feeling as though you're carrying basically nothing underwater, like minimalism, and you don't mind weight belts, do the Halcyon (if you like integrated weights, I'm pretty sure Dive Rite integrated weight pockets would fit on the nylon without a problem). I'm not really sure that the added features of the Hydros are worth the price but I have heard good things about them. Neither should give you trouble in cold water.