Hi Tregy,
Thanks for the message.
Yes we’ve been getting on great! I love it!
I’ve been recording usage (manually) where possible and so far, average daily usage is around 3.4kWh with the heating off (just a hot water) and 10.6kWh with the heating on.
Although, apart from reducing the HW temp (because it was too hot!), I’ve been really bad at optimising the system so I can definitely improve those numbers with some effort.
Those usage numbers mean that the annual cost should come in just below gas, which is very pleasing.
It works great! I use the central heating on a timer. The radiators don’t get super hot so it takes longer to heat the house, but not that much longer (1.5hours on a cold day, maybe?) - it’s normally set to 21° where the thermostat is (individual rooms vary a bit).
It is actually possible to get the radiators very warm (hotter than I thought), but I’ve not because I’ve been trying to be economical.
I do miss my nest thermostat a little (for remote/internet control), but I can upgrade in the future to an internet connected thermostat, I just don’t have the money right now.
The RHI payments have worked out more than we expected so we will infact be able to pay it off with just those payments, and have left over.
I would recommend insulation however. Our internal wall insulation I did myself and made a big difference in the coldest rooms, it wasn’t that expensive (plus we did one room at a time).
You could always do the insulation after the heat pump, it might even work out better for you in terms of your EPC rating when you apply for your RHI payments 
I plan on posting some of the findings online when after winter, and will post back here when I do that 