Got this system for Christmas, works wonderfully with a very high connivence factor. When activated for ~3 hours (at which point it is off most of the time) my oil temps are at ~80 deg with the plane ready to go by the time I taxi to the end of the runway.
Pros,
Heats entire engine compartment, block, oil, battery etc.
Thermostatically controlled, can be left on with no worry of over heating.
No mods or stuff attached to the engine.
Cell activated remote switch is fantastic (perhaps the best part)
Cons,
NOT cheap (this rig ~$800 with switch)
Not particularly portable (though does fit in the baggage area)
The unit uses a simcard from T-mobile that will run ~$10 for three months.
Comments,
You can get effectively the same switch for ~$200 and connect to some block heaters from Amazon to get roughly the same setup for ~$250.