Just to answer my own question, since nobody else did, I measured the resistance of the heating elements in these mirrors and the stock ones. The resistance in these is 1/2 the stock heating lement so it's no wonder they are just about useless as heated mirrors.I'm interested in feedback from other people who have these installed as to how the heating seems to work compared to OEM. Mine don't seem to have any warmth to them and don't seem to have had any impact through the recent snow, whereas the OEM mirrors worked quite well.
I guess I need to take one off, reinstall the OEM mirror and do a back to back comparison. The Blindspot element certainly helps, although it is nowhere near as distinct as it is on OEM mirrors, but I need the heating to work effectively
My 2 cent, save your money and buy decent OEM mirrors, these are junk.
And "To The Top" it goes.