I use Rancos and the one thing I really like about them is that they automatically reset if there's a power outage. In the summer I can turn mine off for months at a time and I don't even need to reset anything when I plug them back in once the weather cools off.

My suggestion, if you're looking to save some money, is to look for them through HVAC suppliers rather than pet supply places. I got my Ranco ETC111000s for under $50 apiece from HVAC suppliers, and they're over $100 on some pet supply websites.