Ranco controllers are the safest if you're thinking about using a device that isn't proven.
Ranco makes devices for Commercial and Industrial Refrigeration. The same controller that we use for our heaters and chillers are used to protect/cool Millions of $$$ in produce, meat, fish and a lot more. So the $100 +/- single stage Ranco Model # ETC-111000-000 is cheap compared to the $100,000 that a restaurant may have in their walk-in cooler.
You can even OPT for the more expensive model which is WATER-SAFE to be on the safe side as we all spill water once in a while.
Ranco, by far is the best choice. Every other option is ONLY a "hobbiest" toy compared to it.
I know it sounds pricey, but being that it is proven and responsible for keeping things at temperature that can go far beyond the price that some of us may have in our tanks, it's the safest way to go. And even the single stage unit can be programmed in the summer to operate a chiller or even just control a fan to blow over your tank/sump just for a little added safety.
Best of luck on your search!