Thanks GPS - that was helpful info on the indicators of running too hot. I think you're right, I'll probably be fine running with just one out for the summer. After all, northern Alberta temps are not the same as someone might see in Arizona.

A couple people have mentioned A/C - I never use it, at all. In the summer I will roll down the windows. I will use the heater in the winter but I "non-A/C" guy.

Unfortunately I can't give you any insight on how the inserts affect winter MPG - I've only had the FEH for about a month now (just over 800km) and I just put the inserts in last night. I can say that today is seemed to hit EV a little sooner, especially those times when I parked it for a bit and then came back. That could just be me though.

Oh, and someone had asked what the installation was like - I'll take some photos when I take the one insert out.