Choose one from a large, established company.
Some years ago I invested in security cameras that no longer work because the company folded and the cameras would only work with their software.
Honeywell is my favourite from this list of five but it is not cheap. You need to decide what you need it to do before you buy
https://www.techadvisor.com/article/723403/best-smart-thermostat-2.html
I don't think I would bother with a smart thermometer, really. Unless your life is unpredictable and the house unexpectedly empty often then I really can't see the point. My manual timer must be 20 years old and is still going strong, I can't see any smart meter lasting anything like that - after a few short years it will be unsupported by the manufacturer and be useless.