Electric water heaters can be mounted high on a wall or under a cabinet.
Electric instant water heaters do save money by not losing heat as does a 40-gallon vessel sitting all day throwing heat away.
Unless the electricity is produced by a dam or atomic energy, the electricity is produced by burning a fuel. the line losses transmitting the electricity are high; so most electric rates are 3 times the cost of providing the heating by burning fuels in the home. Cutting the electric bill in half by making the electric usage more efficient still makes electricity more expensive.
The typical family bill for gas or oil hot water is $250 per year. The typical electric bill for the same hot water use is $800 per year. Cutting the electric bill in half still makes it $150 per year more expensive – and the cost of installation of the point-of-use electric heater is very high.