I think the whole point of using flexwatt is because it saves you money while being more reliable that most UTH. The savings part is especially true when you have a lot of tubs to heat

I use a herpstat ND and am VERY happy with it. You should get a thermostat BEFORE using any heat source. Most of them will allow you to hook up mulitple heat source when purchased.

I don't know what a 100 watt CHE is. But just stick with "Flexwatt" heat tape. It's a proven product.