Thanks Freak!
I am aware of all the potential drawbacks, but in our home it's just 2 of us so I don't think having enough HW would be an issue. My primary concerns are the upfront cost and maintenance. Nothing I can do about the up front cost, they are new and cost are pretty consistent across the board.
After looking into them a little closer, most all of them require you perform yearly maintenance to keep your warranty. The maintenance, about $150 a pop, they do is pretty much a vinegar type flush to rid the unit of calcium deposits. Something I could do myself, but it must be done "...by a certified technician..." or you could void the warranty.
I really like the idea of not heating water when I'm not using it... I just wish the technology was perfected.
J, AEP rents these things???
Yeah they are pretty neat, and the Rinnai mounts on the wall.