We just started a mini class at our local track and it has been great so far. I built up an M05 and it was a fun build. I had a large supply of hex head 3mm screws to replace most of the phillips ones that come with the kit and I pretapped the holes in the plastics (more durable in my experience, plus better with my carpal tunnel). Only non-stock items so far are the titanium king pins (mostly due to them not being phillips heads) and a set of left over plastic (but oil filled) Sakura shocks and the Tamiya short TC springs to go with.
Car is a hoot, and with the stock setup (adjusted ride height so the lower suspension arms are flat), the thing was cake to drive. It's slow (new unbroken in motor and a questionable nimh battery), but was a blast.