I just switched from a $150 Smart thermostat to a $40 Smart thermostat and it’s been working better than the more expensive one. Go figure.
As for exposing smart devices that aren’t native to SmartThings, I have some air purifiers that aren’t directly connected to SmartThings, but they are connected to Amazon Alexa so I don’t have to use the manufactures app. I setup SmartThings virtual switches (@TAustin style) with either contact or motion to turn On/Off via SmartThings Routines with Alexa Routines that can use either the contact or motion from the SmartThings virtual switch as the trigger to turn On/Off the air purifiers.