yes and yes.
Done correctly, correctly sized etc it's a winner. As anything. If customers are asking for it, then it's a winner.
Sell it honestly though. It's not for the single old lady in a bungalow with only a shower, it's for the family with a couple of kids etc. They get the benefit and a very realistic payback.
Also, for businesses, they can get a carbon trust 0% loan to pay for it....
Good luck.