Been looking at these : http://www.northerntool.com/shop/tools/product_200339107_200339107 The reviews are mixed. The theory is good. Keeping the tranny warm would sure get my loader moving better in winter.
I have one of those for my Holder (air cooled deutz) and it is rather pathetic. plus I am always worried about an oil leak starting a fire. I think that they are only 450 watts and that is not direct into the oil. it does not transfer the heat too well
The link is for a 10 volt 300 watt heater? I'd think this would drain your battery in no time. A 200 watt lamp in a holder under the transmission would work better, in my opinion.
I tried one of those heaters on my 544 Deere, didn't work all that good, I too was worried about it catching fire.