Forgot to mention, this decision is made more complicated as I have the legacy Nest integration in SmartThings, so I can currently manage the Nest in ST to do the key safety actions (turn off if smoke/fire, turn off if leak, etc.). One of my options is to just leave the Nest and my smoke alarms and AC leak sensor on ST, and not try to move that stuff over to HE. But then I can't integrate any of that stuff into HE. (HubConnect is a complete fail for me, tried w/lots of help and it just does not work for me for some reason.)
The Honeywell T6 Zwave model (Honeywell TH6320ZW2003 T6, not the Pro version which is Wi-Fi only) also looks like a very interesting option, and @bcopeland has written what looks like a very nice community integration for it. Looks like some have found it for $80 on eBay.
