Answer: -My dad was considering one, the overwhelming majority said they only last 5 years and most cannot keep up with **heavy** demand. -My relatives had one when they lived in England for several years and it worked just fine. In most parts of the world with higher energy costs than the US, on-demand heaters are the standard. -I havn't heard many comments from people that own them. Comments from plumbers have been mixed. There are two problems that I'm aware of, a longer delay before water at the tap is hot, and the volume of water if the demand is high. I'm not sure the latter is unique to tankless heaters as with my current 30 gallon tank the morning shower will be on the chilly side if anybody else is using hot water. I heard a number of years ago about someone putting a 6 gallon gas water heater tank in front of the tankless heater to solve the delay problem. The problem of quantity of hot water seems like it could be solved by buying the next size larger unit. I have an older house that dosn't have the 30x30 inch clear access space in front of the water heater required by code. I'd really like to upgrade some of the plumbing, but if I touch one thing, the whole house has to meet code to pass inspection. One solution would be to install the more compact tankless heater in the attic.