The thermostat on my 110v SoftTub Hot Tub went out and there's no replacement available. If there were, it would be over $100, and I'd have to hire help to put it in.
This genius device solved my problem for under $30. So far it works great outside and tracks the temperature better than I hoped.
Now my biggest worry is over, it heated for at least 8 hours without issue. I worried that the tub might pull too much juice, but it doesn't seem so.
I bet there's a million and one things you could use this for.