I have one. It does not work with ST. I too wish it did, as otherwise it is a very nice device.
I have asked Intesis about api access, really nothing coming as near as I can tell. They do some stuff with ascii locally, but this is a problem with ST to do bi-directional communication. Ideally they would offer a local rest interface, or a cloud interface, but alas none I see in sight.
The zxt120 is a “bridge option”. It can control many of the hvac systems (well at least mine), and has a dth that works with ST. It’s challenge is it is an early zwave device (talk only), that does not “report” real status back from the hvac system (it can report temp at the zxt120), and it can “tell you” the last command it sent (i.e. it assume you would never change state without using it). This can be a pain when the family uses the hvac remote to do some changes (or you make changes via Intesis).
I have found that with an intesis, and zxt120 you can control the system from ST, and the intesis does a good job of telling you (but not ST) what the hvac system is doing now (it is a bi-directional communication device when properly installed). I.e. if I change things with the zxt120 (or the hvac remote), the Intesis knows (in its mobile app). However if you change things with Intesis, neither the hvac remote or the zxt120 have a clue.
Not pretty having two devices to do the job of one…but that is all I have found.
Intesis could own this space if they fixed their api access.