I haven't seen a whole house electric unit but from what I have seen of the point of use elements I wouldn't install any of them in my house, nor recommend them to a client.
I've installed a 30A and a 50A unit. The 30 was worthless above flow rates more than a trickle.
The fifty was installed where the ground water gets cold and the house had a loooong overhesd service drop.
Result was to pull the mains down about 9% while providing just enough rise in water temp at an almost tolerable flow rate to wash your hands. I checked out the one in a friends office restroom and it was the same story. 50A, dimming lights, poor rise in temp at any kind of flow rate.
I have wired a couple of houses that use gas whole house on demand units. Both houses were long kinda long in design.
Both houses have 2 units feeding the hot water line at opposite ends of the house. One of the units didn't even need the receptacle I installed for it because it used a flow powered generator for ignition. I was impressed with the performance of these systems and the homeowners seem happy with them.
If you can go gas and think about 2 units if you have long hot water pipes.
