Electric tankless water heaters draw more power than a storage type water heater. Their operation could cost more if the local utility company charges a higher demand rate. With both electric and gas units the electronics are extremely more complicated than a storage type water heater, it's similar to comparing an old 1960's American car to a new Toyota, so maintenance is more complicated, and they require more attention. Most electric on demand or point of use water heaters don't supply enough hot water for regular use like taking a shower, or using the dishwasher. Their best use is for sinks like an office sink or a sink in bathroom for washing hands. Although the label on the electric unit says "Whole House" they can really only service a single shower use and a a few sinks.