The cheap ones are fairly common in Britain where the user isn't choosing (student houses, cheap rentals etc). The installation cost is low, but the running cos

The cheap ones are fairly common in Britain where the user isn't choosing (student houses, cheap rentals etc). The installation cost is low, but the running cost is high. They are crap. 8kW is typical, and the pressure for a reasonable water temperature is low. I haven't knowingly used a more powerful one. I suspect that would negate the cheap installation cost, as it would need a three phase circuit.