Yes, I think it would be better/safer to get a heater without an internal t-stat, and use your own.
For piggy backing, you plug one into the heat source, with the temp range you want.
Then, instead of plugging that t-stat into the wall/power source, you plug it into another t-stat, with a couple degrees more of a temp fluctuation (not sure if my explanation makes sense).
If the one directly connected to the heat source fails, the backup t-stat keeps it from over heating.