The benefit of a point-of-use heater is that you do not need to send hot and cold water lines to each fixture. You can send one larger water line to the shower heater and other single lines to electric heaters for the sinks. In this manner, you have no heat lost from the hot water piping, hot water is produced at the location it is used.
Downsides are that hard water will clog them quickly and cause early replacement. You have chosen the most expensive form of heating as electricity is 3 times the cost per heat unit of natural gas or oil. (LP gas equals the cost of electricity.) You can achieve reasonable utility costs that are equal to natural gas or oil heated homes by superinsulating your home. You can also cut the cost of utilities by 1/3 by superinsulating and delivering oil heat to your home.
It now costs a typical US family $800 per year to make hot water with an electric hot water heater tank. This might be cut to $600 with a tankless instant heater as the heater or pipes lose little heat. Hot water made with natural gas or oil boiler and heat exchange tank would cost $300 for the same family.