I've never used a heat mat, and never will. I have my BP set up in a 3ft wooden viv with a single CHE on the hot side. Temps are fine across the viv, humidity is fine and she is as healthy as can be. Consistent eater, consistent pooper, consistent shedder
I personally don't know why so many people harp on that heat mats are essential. If you have a RUB/rack setup then yeah - you've got nowhere to mount a CHE and it's easier/cheaper to heat numerous RUBS off of mats. If you don't and you can maintain heat and humidity with just a CHE then that's all you'll need