Thread is a little old now, but thought I'd add a few thoughts for anyone looking into the Zuma.
My wife and I both have Zumas (her's is the SM, mine the Med) We've taken them on three trips now requiring flying (BVI twice for 10 days each time and to Key Largo for a week) so we have over 40 dives each in them. Travel hasn't been an issue of course - it packs so small it pretty much dissapears in your bag. Function is really good, as others have stated, but I've found a real challenge with the fit. My wife's fits her perfectly so she has no complaints at all, but mine just doesn't fit right. Everything you'd want it to do as a travel BC is great it seems if it fits properly. For me (5'-8" and 30" waist) it just doesn't seem to work out - and the small just doesn't have enough strap for my hight to get the belt to my waist where it belongs, not to mention I'd have to ditch the chest strap because it would choke me. Given the way it fits, I run into the same problems mentioned earlier with things like trying to balance out. The ditch weights slide way around to the front, since I have to cinch up the belt so far, creating some real problems that I blance out with some weight on the tank. After tinkering with it for a year, I can level out and float at the surface the way I want, but it was a bit too much trial and error. Dumping air is also a problem depending on how it fits you, the upper dump valve on my wife's is in perfect position to dump the bladder, but mine sits far enough back that I have to twist and turn to get the bladder empty - I've seen this with another person as well in the Zuma - it just didn't fit him correctly either.
All in all, I'd agree that most of the positive comments in the thread are accurate, you just have to be the "size" that AL designed the Zuma for or you'll run into the "fit impacting function" problems I have. As for my wife, she wouldn't dive in anything else - for me, I've picked up an Apeks WTX and stripped it down to the basics so I can travel with it. I'm not ditching the Zuma, it's just not going to be what I grab first in most cases I believe. I'm holding out that AL adds another size with the same over the shoulder dimensions as the Med but with a more athletic build in mind.
