Minitank Water Heater
Instead of heating a large quantity of water, a minitank heater heats a small amount. Thus, it is capable of higher efficiency (less heating loss) compared to a full tank water heater. Its advantage for off-grid use (assuming limited electrical power) lies in using a small heater element - unlike tankless heaters (on-demand heaters) - which require much more power (4-8kW) compared to minitank (1-2 kW). Disadvantage is that you run out of hot water if you use up more than the tank - say a long shower.
From a critical perspective - it is about 1.5 kW - worst of 2 worlds - don't have enough continuous hot water, and waste energy. You can tell by their larger size than true tankless.