Eccotemp makes the InstaHot and is way cheaper to buy without the Schneiders mark up.
I have the L10 for $175. Setup took 15 minutes. Endless hot water. Super easy to drain with quick connect hose fittings. Good pressure. I tried both a coil hose and expanding hose and much prefer the expanding hose. Better pressure and no tangling.
Electric on demand heaters take a tremendous amount of power that a small barn’s electric panel is likely not designed to handle. This poses a greater fire risk than a properly installed propane water heater. The temp rise is not high enough at higher flow rates.