I have been using this water heater for 10 years now. In these 10 years I have not faced a single breakdown. I use a bathtub and the water needs to be really hot to fill it up. I never had to wait for a second round. The performance has been efficient and consistent.
The hot water in the heater stays hot for 12 hours and I take a shower again without having to heat the water again.
A great saving on electricity.
It would be a great idea if boilers could be provide with temperature controllers so that one can heat the water to the desired temperature.