Does anyone have a feel for how well this works?
The biggest complaint I have seen is that ST uses the cloud (except for the most common Zwave devices) including the ST-MQTT-Bridge. This can result in 1) delays and 2) non-functionality. For example I have a sensor that turns on a light and this can take from 1 second to as many as 10 seconds. If your internet connection goes down, or the ST cloud servers have gone down you can loose functionality, but I have never experienced this (yet).
As for device support, ST writes “device handlers” that the hub uses to support many common ZWave devices, and there are lots of “device handlers” developed by the community. There is a large community for ST, so chances are you’ll find a device handler for your device. Nevertheless, I always look to see if a device handler has been written for a Zwave device that I’m interested in.
Another problem to be aware of is when a single ZWave device has multiple instances of a function, say multiple buttons, you may find a device handler that supports the multiple buttons but it either can not communicate more than one button to the ST-MQTT-Bridge, or the ST-MQTT-Bridge can’t handle more than one (at least as far as I’ve been able to figure out).