I've been using a Competition Heater since the day they launched the 110V version. This thing is AWESOME! It reduces engine wear a little by pre-expanding all the engine components before ya spin em over. It makes starting a Nitro rig SOOOO much easier....and once it fires...you are pretty much ready to race/tune/bash. No warm up time needed. The engine is already just about up to temp for you.
Eric (the creator) is an awesome guy as well. Came from the NASCAR industry and really knows his stuff. It's probably the best $100 I have spent in awhile....
Oh and I use it ALL year round to preheat my engines. I leave it on most of the day while at the race track as well. It really heat saturates the engine and chassis 100x better than a heat gun or hair dryer as well.....and works wonders for engine break in. There really are no downsides...other than needing something to power it with ;-)