I found the partially inflated inflatable to conform to the curves of the hammock and me much better than a CCF pad, which tended to buckle instead. I also found the inflatable to be plenty warm enough ... where it was under me. But any part that hung off the pad and against the sides of the hammock? COLD. I used a seatpad and various pieces of clothing to insulate my butt and knees, but they had to be shifted every time I turned over. A pain in the butt.
So, that pad will work, and better than a CCF, but not nearly so well as an UQ, based on my experience.
As far as using an REI sleeping bag for a TQ, I did the same thing for a long while. But half the bag is barely insulated at all (the bottom half), so you're not evenly warm when using it as a TQ. Just FYI.