I have the Halycon stainless steel and aluminum backplates, an Eclipse (30 lb.) wing (which takes the Halcyon single-tank adaptor) and an older "Pioneer" (27 lb.) wing which can be used without the STA, simple webbing (DIR-style) harnesses on both. On both harnesses, I have two small square pockets on waist band which I have made by someone here in Bali (they are much smaller than the Halcyon pocket) - one carries a spare mask, the other an emergency strobe, dye pack, rolled up hat with neck flap and a reef hook.
I prefer the stainless steel BP and also like the Eclipse with STA better than the the STA-less Pioneer. Without the STA, the tank sits too close to the BP (and the back of my head), my hose routing doesn't work as well, etc.
The stainless BP is mainly for local diving here in Bali and/or trips originating here. If I have to fly with dive gear, then I take the aluminum backplate. For doubles diving, which I do very rarely, I borrow or rent a double-tank wing and use it with either backplate, usually the SS.
In practice, the aluminum BP, the STA and the Eclipse wing spend a lot of time on boats or in transit without me. Since I've done two trips on the Seven Seas this year and will do a couple more over October/November, it has made sense this year to leave a full set of dive gear (BP and wing, fins, reg set, etc.) on board, minimizing the amount of gear I have to shlep via small planes.
Living in Indonesia, it isn't really practical for me to source dive gear from small independent manufacturers in the US like Oxycheq or FredT, so I'm not in any position to compare their products iwth Halycon. I basically like Halcyon equipment, but the critical factor for me is that there is a good Halcyon wholesale distributor nearby in Singapore, my friend Avandy at BIDP is a dealer so I can get some stuff here in Bali (though I usually have to bring anything in myself from Singapore), and Halycon gear is also available from dealers in Hong Kong and the Philippines. (Once, when I had a minor problem with a Halcyon wing, Halycon airshipped a new wing to me within a few days.) However, I had to pay duty on that.) If I lived in CA or FL, it might be different.
(The last conventional BC I owned was a Seaquest Balance too.)
Frogfish
P.S. Weights. In warm water, with the stainless BP and a 3-mil wetsuit, I only need a couple of kg on a belt under the harness. With a 5 mil, I add two more kg in trim pockets on the lower tank camband. With the AL BP and a 3 mil, I will have 2 kg in trim pockets on the tank cambands and 2 or 3 kg on a belt. With a 5 mil, I carry 4 kg on the belt. Diving doubles, it depends on the size and weight of the tanks, of course, but if they're steel, then I won't need any extra weight.