I would avoid the surge protector type power strip. They could activate during one of the up down temperature swings the system does in proportional mode and leave those tubs without heat. If you have the Pro or Herpstat II they have alarms, so if you set the alarm and were home you would hear it and could do something, but the basic herpstat doesn't have this feature.

I've used the inexpensive simple power strips that you buy 2 for 5 or 6 bucks at lowes or Home depot for over 2 years without any issues other than if you plug and unplug things too much they may start to wear out.