I've never used the flexwatt tape either.
Right now I just have the DIY rheostat hooked up (which consists of a regular dimmer switch used for lighting). According to my temp gun it's 83 degrees on the warm side (the back) and 77 on the cool side (the front) which is just about perfect for the corns I plan on housing.
I've only just plugged it in a couple of hours ago so I suspect I'll have to do some fine tuning but from my observations thus far the flexwatt doesn't get nearly as hot as some of the heating pads available on the market today.