OK, don't shoot me but I have one.

To be fair, the house it's in is designed for it (18-inch-thick insulated walls, a heat recovery system, a small PV system, triple glazing and underfloor heating everywhere).

What I found at first was I couldn't get to grips with it and that it was totally frustrating. It took me a while to realize it won't work if you want instantaneous "on-demand" control. You have to leave it on almost all the time and draw from the slowly collected heat as you use the hot water and heating during your use of your house over a 24-hour cycle. Essentially, it's a system for people who are willing to plan.

It's actually very quiet. The house is cozily warm all the year and it's very cheap to run - my total electricity bill is less than 450GBP a year (I don't have gas).