Recent trip with Hydros. Easily packed Hydros with integrated weight pockets, mask, regs and camera gear (Oly TG-4 with housing and SeaDragon strobe) in carry on and "personal bag."
Added a pocket to my Hydros by hanging a pocket off the back of the colored weight pocket cover (detach rear screw/attachment point and slide pocket on). Pocket a bit hard to access but still usable. Contained large SMB, reel, folding knife and flash light. Only real problem was late in trip I must have sat on it on dive boat. Rear attachment point pulled out of the rubber. Pocket didn't fall off and no damage to rubber. Attachment point easily replaced. Still...think I'll switch to thigh pocket.
Hung 6cft pony bottle from shoulder D-ring. Tried both sides. Worked well. Pony bottle actually got used once (not by me, I donated it to someone else who had a catastrophic air leak and then wanted a quick dive to 30ft to retrieve a reel). I'm very happy with this arrangement.
Shoved loop of alternate reg (octo) hose into opening in top of weight pocket. Stayed put and easy to deploy. (Got deployed in above-described leak situation.)
Trim was very nice. Only issue was when I had pony and pocket on same side. Caused some roll trim issues. Fixed by asymmetrical weights or moving pony to other side. May have been some issue with air getting a bit stuck on one side. Probably exacerbated by the fact I was overweighted. Issue gone after adjustments to load. At surface, sit back on it, relax and enjoy the view...unless the view is 10ft waves, it's your first-ever ocean dive and you forgot your Dramamine (I didn't puke till I stood on dry land though).
BC rides better than anything I've used before. Even loosely strapped on it never moves. You forget you're wearing it. Rides well out of the water too. Very secure feeling walking loaded up around boat.
Donning was a little tricky for me with the pony on. Even fully extended, shoulder straps grab wetsuit so well it doesn't completely easily slip on. Found easiest way to slip into it was to squat lower than the BC when tank in racks on the boat, then kind of stand up and into it. Adjust shoulders a bit to slide BC down my back. Then do up waist belt. Then cinch down shoulders. Sternum strap optional even with pony on. I always did it up. Once I was used to it, process of donning was straightforward. Donning in water does not have any issue.
Doffing totally easy. No issues.
Rinses very easily. Dries seemingly in minutes.
11 dives. Looks brand new. I've borrowed one from a LDS employee who whores his Hydros out. It gets hard use all over the world. It also still looks new. He uses the harness with small added weight pockets. I'll likely be setting up similarly.
TLDR: disappears on your back. Good trim. No muss, no fuss.