About 12 years ago I had a water heater fire and had to fit a new gas water heater (for heat and hot water) in a small space. The tankless gas water heater was perfect for the space, mounted off the ceiling. I really liked it. The space was cleaner, the heater more accessible, and the heater was very efficient. The thing is, it was a small slab house. I don't know how well they provide hot water for larger houses.
I forget the name brand. It is French. It had a ceramic liner.