the advantage of Reiffs over an oil heatpad is that you can go to the airport for an unplanned flight, and plug the plane in, and by the time you finish prepping the plane a 1/2 hour later the engine is warmed up ready to start (with the high output kit). the oilpads work but need to be left on overnight.
Tanis is good too, but tends to cost more to purchase and to maintain.
personally i have used Reiffs for the last 12 years.
francois