I saw one of these made by Chris Paulick (forgive me if I mis-spelled) and I've wanted one since. But I never got around to trying to build one. So when Dom said he had one for sale I bought it immediately.
I've had it for a couple of months already but haven't used it much, because I haven't had any uke bodies to sand. But now I have, and it works perfectly! What a joy to use. I gave it a couple of coats of shellac and attached the paper with double stick tape.
The handle is of course not moving, that is the whole secret. So it gives you a perfectly balanced sander that works on both concave and convex curves.