There is more than one thermostat called the Drayton SCR, and Drayton with the standard back plate can do up to three zones and have OpenTherm,
in general Drayton is a better product. The back plate may be same
hive to Drayton, but there is a third wiring for Drayton which is one of the few to allow hard wired motorised valves splitting the home into zones, most use TRV heads to split into zones, the Drayton TRV head is considered to be one of the best with algorithms built in to work out how long to heat a room, so it can heat the room faster than most without overshooting.
Hive is an attempt to make a one size fits all thermostat, it has no option for OpenTherm, and it has to be mounted in a room normally kept cool as the demand for heat system stops when it hits 22°C, but at least it does connect to TRV heads unlike Nest, which does have OpenTherm but does not connect to TRV heads.
As far as I am lead to understand you can simply fit Hive on the existing back plate, this has been the big problem, same plate and three wiring diagrams depending if 1, 2, or 3 zones, and even same back plate used for programmer and thermostat.
In the main units have wiring diagrams printed on them, it is up to you to check they match.
