Bosch Aquastar has many units, you can get an old pilot model if you
wish to waste energy or one of the newer models most people buy. 2 of
them require no outside electricity supply, one has battery ignition ,
which I have, and one has a mini hydro generator. I dont see any more
delay than with a tank.

Recirculators waste energy.

Electric tankless heaters for most of the US cost double to operate
than gas and easily require you to upgrade your main as a good Bosch
unit takes apx 120 amp itself to operate.