All that said, there are a few key details I think need to be highlighted which are either potential problems or my misunderstanding. Either way, they need to be addressed.

• Homely specify that they need an extra bit of Mitsi kit installed - a MelcoBEMS Mini A1M module - which is a module that allows the flow temperature controller to talk modbus so that the Homely box can be connected to that module. Looking online I've seen prices for that module ranging between £133 and £207, although it obviously is possible to buy secondhand on eBay.
• The modbus adapter is a little box that plugs into the CN105 socket in the FTC cabinet. I'm now quite familiar with that, having bought a little third party dongle that makes it easy to link with Home Assistant. The CN105 socket is also the socket used for plugging in a wifi adapter such as the MAC-587IF. Unlike the third party dongle, though, the Mini A1M module does not have a second pass-through CN105 socket, so where I can have a little box of tricks for connecting to Home Assistant or similar AND still have my heat pump talking with Mitsubishi's Melcloud cloud systems, it looks as if opting for Homely involves stopping using Melcloud altogether. Either control through Homely or via the Melcloud app but never both.
• Because of the either/or choice of Homely or Melcloud, it will not be possible to have Homely controlling the heat pump and Melcloud giving the stats.

I hasten to add that this is not a criticism of Homely. From what I can see, this is entirely the result of Mitsubishi not designing their wifi adapter or their modbus adapter to allow operation in parallel.

And further Mitsi specific info here:

https://www.homelyenergy.com/homely-mitsubishi-heat-pump-integration/?utm_medium=email&_hsenc=p2ANqtz-_NaPdB750cRph_UT0cdbn2Tdbz8TupUgRDPLPTdOWHTntr1RKsaSkNCRx219Ky4Kg_HNDCCOdwaBBCGTev3lsV-kVi40ScmTY0S18x7Q55JHej8OY&_hsmi=402676911&utm_content=402676911&utm_source=hs_email

Regards, Toodles.