I’ve no experience of this myself, but it looks like it’s possible to get some data from a Grant ASHP via modbus. It sounds like the Grant Aerona3 has modbus built in as standard, no additional module required.
Unfortunately looking at the list of registers available, there’s not enough data to calculate COP. For that we would need FlowT, ReturnT, electrical power and flow rate. So it looks like a 3rd party heat and electricity meters would still be required to enable COP to be calculated. But it may be possible to read mode registers that are not documented yet?