I have a few .55, 1.0 (cc) plus a few of the .09 and .15, all in RC version. The engines work very well but the carb is a little too crude for my taste, they work even better with an adjustable low end.
Here is a short video of a .09RC in a Thunder Tiger "Scooter";
http://rcuvideos.com/video/TT-Scooter-with-PAW-09-RC