I like the idea that there's a gas boiler built into them, and the controller knows when to use it, versus using the ASHP part .. the only bit I can't quite understand is why it's built into the indoor unit. If it were in the outdoor unit, it would do away with the flue, it could be a tiny boiler, and it could heat the refrigerant

SInce finding this out, I can't help but think it's not so much a unique selling point after all - why bother integrating it into the indoor unit when the unit could simply be made smaller, keep the intelligent control of ashp/boiler mode and have a switched/voltfree connection to command a separate boiler?

It's convertible to LPG (and promoted by Calor) for those of us not on mains gas ;)

It's one thing I didn't quite get about the Calor offering - the install price for the pump also includes the LPG tank and all its connectivity and they'll even bury it if the customer digs the hole. I got to wondering, if the pump is correctly sized for the house, it'll use the gas next to never so one fill up will go a very long way. For a gas company, unless there's some rental element to the tank and it not just be built into the litre price of the gas, this action must be a foot-shoot in some regards..