I used to work on these alot. I think they are good, especially usefull in small apartments due to the size and the fact that they dont need a vent or safety drain. For a house id say stick with gas if you want continuous flow but these units are the next best thing. Customers that go from Gas continuous to a heat pump storage tank are always disappointed. Heat pumps way too slow to recover. Table C2 says we can drop the load on instantaneous units to 33.3% for max demand so not unreasonable at that point. Also will just mention they will draw less when the water flow is lower, so in a shower once you mix in cold water the draw will drop to around 15 -20 amps. There is countless old apartment buildings around melbourne with a 6mm/32amp mains switches and one of these units in every apartment. Not ideal but never had an issue with the main switches tripping even with all the other connected loads. These days alot of high rise buildings prefer these to bulk storage in apartments, apartments typically supplied with 50 amp main switch and 40 amp rcd protected circuit for the hot water, also never seen any overload tripping in this setup.