I have a CDX5 Delta 3 and a CDX5 Zeta and I love the Zeta. It took three trips back to my LDS to get tuned, but ever since that, it's done about 12 dives without hitch. No free flow, the best air delivery I've seen (on about 6 regs I've used).
When you want air the Zeta delivers without hitch, meanwhile if you aren't huffing and puffing it only delivers what you need. All regs are pretty much demand based, but this one requires no adjustment. I've taken it down to 110' and it breathes just as easy.
It has a different design than a traditional reg which seasoned scuba divers are not keen on, hence why it didn't sell too well, but according to a customer service guy I spoke with at Oceanic, a lot of the Oceanic staff dives with it and they love it.
My air consumption is really good considering I'm a 170lb male. My g/f used to end dives with 1200+ PSI but now we're just about even. All this happened when I switched from the Delta3 to the Zeta so the rumors about people consuming too much air on the Zeta or false, either that or they're just sucking in way too hard because the Zeta will deliver (which is nice if you're doing something physical underwater), work, chasing something, etc...