Great for putting on the side of your fermenter be that plastic or stainless to give you a good indication of what your fermentation control and temperature is like.
Stainless is a great conductor of heat so adhesive thermometers like this are much more accurate on Stainless fermenters than they are say a plastic bucket.
Either way remember the immutable laws of Brewing! Rule #3 Temperature Control. With these little friends on the side of your fermenter you can monitor your ferment temperatures like a pro!