My 2 cents on topic - I'd use a heater any time I could for at least a couple of hours before using the machine when it's cold out (below 20 F). It can only help. Don't know about using it and then not starting the machine, I just don't do that. BTW, I have the JD factory block heater on my 2520 but I'm thinking it sure wouldn't hurt to protect the pumps and tranny with some heat too. So I'm planning to install a tranny heater but I know I can get one cheaper than the JD. The JD heater is just a screw in heating element that goes into one of the holes in the back of the tranny near the sight level window. It literally gets bathed in oil. A suitable one can be bought from any industrial supply like Grainger for way cheaper than JD gets. In the next month or two I'm going to find a direct replacement and I'll let post about it, unless someone else finds one first. This has got to be better than any magnetic or glue on heater and I bet they can be had cheaper by going this route.