SaunaBox or similar "cheap" saunas

What’s the general consensus on portable saunas like the SaunaBox? At less than $350 I don’t think I’d expect much, but are they actually useful? Max temp is 130F.

Probably better off to get a Core temp sensor and do heat training that way. They are doing a big marketing push, but like any other “things” we can buy, using it properly is key to getting one’s monies worth out of them and the benefits.