Hi, we have one in a new build, super insulated house with underfloor heating. It has been a nightmare, the last 2 winters electic bills have been £3000 from oct - may, each year. The unit itself cost £8000, then instulation on top. Ours is made by a company called grants, and they do not employ any engineers in Scotland so you have to wait for an engineer to be able to travel up, we have needed an engineer on at least 8 occasions and in the end had to get a new unit, so haven't tried it this year. We need to top up water temp with emmersion. This has been our biggest regret and my oh wants it changed to oil.
My advice is to think long and hard and if your passing through angus, you are welcome to pop in and see it.
Mojo