I've had one of each, the early single action only version and the newer double action only design.
The earlier version was a very compact pistol, not too bad to shoot and the one I had was pretty reliable with just about any ammo. I carried it as a 'back pocket carry' piece for several years.
I ended up trading it to a friend who just had to have it, and I bought a new, double action version. I ran a box of ammo through this gun and began carrying it. About 6 months later, I went to shoot it and it absolutly would not feed any ammo. I don't know what changed or broke, but it was a single shot firearm. I got rid of it shortly thereafter and bought a Glock 27 to replace it (OK, so it was a little bit bigger :wink: ).
I would not trust one of the DAO Backups for any reason, but that's just my opinion. My current 'back pocket carry' gun is a KelTec P32, and it does a fine job in that role.