I have custom cork foot beds. They were a cork sole that had extra cork and glue added to it, and it was custom molded to my feet using heat and vacuum. The Sidas heater was added to the custom foot beds by digging out spots for the heating pads in the top of the foot beds, the fitter couldn't get the heating pads as far forward (under toes) as usual because the foot bed was too thin there.
I had delayed this addition to my boots for years because I was afraid to ruin the fit. By all accounts there would be no noticeable effect. However, I did notice a slight "gas-pedal" effect, but it was slight, and easy for me to adapt to. As a matter of fact, I kind of like the effect for SL turns.