Sorry for the late response. Been busy with my other online endeavors (normally, this is where I would plug my site, but, that could be kind of crass if you don't know many people here). I've used FIMO and Sculpey on numerous occasions. I made a Spielberg medalion when I was in high-school out of Sculpey III, and I've tried to make a statuette out of the lead character of Aliqat: The Journies of the Seventh Sun, one of my comics I want to launch on my site this year, but I ran out of the stuff.
Just never tried to use it with puppets. Then again, I've never made a puppet with a moving mouth or anything. I've had designs since I was a kid and even perfected different character voices in different octaves, even a plan for a Beakman's World/Clyde Crashcup-like series involving this one scientist character of mine, so if this whole comic writing/drawing thing don't work out, I have other talents to fall back on. I'm kind of envious of the stuff you and a whole lot of these guys and gals can do. Hopefully, I'll find time to learn more of the secrets of the craft because, well, puppetry is a beautiful artform.