Electric DHW? I doubt anyone wants 6-12 small EEmax or Ariston heaters all over their house at points of use. That would at least help limit electrical demand.
Since the heating element is completely immersed in a electric heater its always been about 92% efficient. However, to meet whole house demands with a single unit forget the Powerstar 115/125 series and go to a Seisco 24/28.
But you'll find the unit needs up to 150 amps to service itself under high flow. Consider in my day an all-electric home was considered 200A you'll need to consider bringing in a 300 amp service to avoid conflicts under heavy flow.
So before you get that good Plumber in to size the heater, get your good Electrician in to see if your utility will even go up to that size service given the usage.
Also have the BMW of Water Conditioning as completely immersed the Electric DHW units can really foul a heating element if not fed SOFT WATER.
You'll have a search as people like myself who correct bad installs are few and far between and the people who dot every i and cross every T in following installation requirements barely exist and if you want this unit working OK 5-10-15 years from now you can't skimp on unit or installation. Other than that...electrics are ok. They're tankless versions of electric tanks you've had for years but they recover(produce) at 3-4 times an electric storage heater does.