Reiff is excellent.
Personally, after a lot of study on the subject, I keep my plane (which is in an unheated hangar) with its Reiff Standard System (100W sump plus 50W/cylinder bands) plugged in all the time, mainly because I usually decide to fly without enough time to plug in far enough in advance to be effective. I also vent the crankcase, and I have cowl plugs and a blanket over the cowl to help keep the heat in as well as the engine evenly heated.
It's working so far. I've had the plane for 10 years now and I'm 300 hours past TBO and have no abnormal indications in the oil analysis.