A poorly cared for stretch of heat tape (e.g. one that has been folded accidentally) can have a break in the laminate, which could cause a short with the foil nowhere near the the connections. And yes, the thermostat is the important part, but if such a break occurred, there could be a localized heat spike at the short ten inches away from the probe, which the thermostat won't be able to prevent. My point is, as long as everything else is set up and cared for properly, the difference in safety risk between duct tape and foil tape is nominal at best.