I've just bought and added one of these to my home assistant (2020.12.7). Works well with my heating only system (will trial on A/C this summer).
Nice to have smaller footprint and simplicity than the colortouch models.
edited the "hold mode" statement to be preset_mode. Changed the 'off' preset_mode to 'none', and added the 'away' preset_mode. Confusing to a relatively new user since hold mode isn't in the states dev tools or general climate documentation, and 'off' isn't a valid preset_mode
Add ColorTouch T7850 as a supported/tested thermostat as well as list the currently tested firmware version VH6.79. Add a note how to enable local API.