Personally, I wouldn't get one, but my significant buddy's dad has one. I would *strongly* recommend practicing with one if you do go that way. Feel what it's like to breathe off it (and if necessary, adjust your hoses, straps, or whatever), and practice manual inflation/deflation of your BC with it.
I've heard that you can deflate your BC while using the integrated regulator, which is something you'll really want to know (as you don't want to be sharing air in an emergency and then add an inadvertant potentially-DCS-inducing rocket to the surface).
One of the reasons I don't bother looking into them is that I've been led to believe that runaway power inflators can happen. In the event of a stuck inflator, I can just pop the LP hose off and keep going with the dive (manually inflating the BC is a skill that has become trivial to me). If I had an integrated secondary reg, in the event of an inflator problem, I'd be forced to call the dive (as I'd have only one second stage remaining, since I'd have disconnected my alternate).
It may or may not be a valid reason to the way you dive, but to me with my diving, I wanted to keep that option open. Also, the inconvenience of breathing off the corrugated hose didn't sit too well with my style of diving (although I could always use the pull dumps in an emergency, so that is also not necessarily an issue for everyone).
Of course, a secondary reg dragging in the sand (as we've probably all seen) isn't something I'd want to have to rely on... but if you're thinking about gear enough to ask about an integrated secondary/inflator, you're probably not apathetic or oblivious enough to dive with a dragging octo (there are *many* ways to secure an octo, after all).
