I agree, can't hurt and might help a bit. I seriously doubt you will see a 20°F difference in the oil tank (please note, they do not claim that, they claim a 21° drop at the exit of the filter). I do wonder just how well it would fit if you don't use a stock Harley oil filter. Since it is only held on by a slight interference fit that is a valid question. Just like any heat sink, it's only going to work up to it's potential if there is good contact over the maximum surface area available. The next question would be, how hard is it going to be to remove when you change the filters?
Look at it this way, where else can you add bling that won't hurt anything but might actually perform a useful function, and all for only $40? Beats all those totally non-functional bits of chinese chrome you'll find at the dealership with the inflated prices.
Jerry