Have this running for awhile now. I have it under my sink. Just hot water for the sink in my office. Since it's only a small office, this works perfectly. It's not made for running hot water for long periods of time. As long as it's for short duration use, I think this will work really well.

I installed this myself. My hot water tank is pretty far away and it took a long time to get hot water. Now I get hot water right away. Works great but I have one small problem. The one-way valve leaks very slowly so I have the hose in a bucket. I tried to call customer service for the company that made it but there is no phone number. Also can't find anything on the internet.
Update 10/20/2022
I researched the leak and found out that I needed an expansion tank on my main water heater. After installing that my leak was solved.

Installed it on my boat and it allowed me to remove the old 5 gallon tank for a battery installation. This one I mounted in the head under the sink. The fittings are odd and a simple pipe thread would make installation simpler. It also doesn't need a 1500 watt element as it heats the water up in two minutes. I would prefer a 750 watt element for a lower amp draw and the recovery rate would still be satisfactory. The thermostat is set very low on mine and the water is still scalding. Overall I am satisfied, but it could be better for the price.
It is a well built unit.

1) I read a review stating the fittings were unique and the reviewer stated he had to search for a week to find them. Once it arrived I checked the threads (connections) Making no comment on the expertise of that reviewer. But, standard FIP braided hoses attached no problem. Also CPVC threaded connections use the SAME thread, thus finding fittings to match is actually quite easy.

2) My situation is unique,
a) I (previously) replaced a 40 gallon tank water heater with a tankless water heater. My dilemma is I need to circulate (warmed) water for freeze protection as pipes run thru an unheated (and a not accessible) space. The circulator pump does not provide enough flow to trigger the start of "tankless" water heater
b) W/O a circulator pump warm water takes forever to reach the bathroom (sink).
c) My wife did not want to give up under sink vanity storage space, therefore we selected an out of the way, spot at the back / top of a linen closet, {photo} the good news is this is out of the way and occupies previously unused space.. the negative is it made installation more complicated.

Solution: this 8 liter (2.1 gallon) 1500W electric heater:

The water to the bathroom is hot quickly
The circulating pump can now pump periodically for freeze protection.

Other comments:
->The user manual is brief and simplistic but adequate.
->The inlet valve is a combination relief valve also a check valve, depending on your installation it is to prevent "hot water" backflowing into the cold water header. This feature is NOT specified in the manual.
-> I have yet to measure the water temperature, but at the mid setting the water is plenty hot.
-> The unit is relatively small, the design is smooth and sleek. But with no handles built in it is a bit cumbersome.
-> Being light weight I plan to remove it annually for draining and descaling.
->Since I "feed it" with the normal hot water supply, there is no recovery time, If i use 2 gallons, it is replaced with 2 gallons of hot water.
-> Insulation is adequate, on the outside of the unit I cannot perceive any temperature different than ambient temperature.

Summary:
This works great for my situation
The price was (is) reasonable
Several similar models made my short list, I chose this one because it included free shipping and was scheduled to be delivered in under 1 week. In reality it arrived 3 days after I ordered it.
Since it is (120vac) electric, no need to run gas lines or exhaust, I do recommend 12 gauge wire minimum with an outlet rated for 20 amps minimum.
I would buy this unit again

I removed the 20yo propane WH in my RV and as old as everything is I'm not interested in spending what a new propane WH costs. Enter this lil guy.

It really is exceptionally tiny so I was able to relocate it to the back of my regular under counter cabinets where a dead space was. This freed up the old WH space which I made a pass through tool storage I can access from inside or out through the old WH exterior access panel.

I prefer boondocking so I have a 24v 400ah bank and wanted to make sure I'm conserving power. The 8 gallon 1,400w electric I previously tried took 20-25 minutes to heat up using 480-580 watts, and ended up being much too big for just myself. Wasting power heating 2X what I needed. This thing also has a 1,400w rating and heats up in 4-5 minutes. That's 90-120 watts used. It's just enough for a wet down, water off soap up, rinse off. With a 4-5 minute heat up it "˜recovers' quickly if I leave the switch on and give it a moment, then I can have a bit longer, or have it ready for another person to use. Ideally a 3-4 gallon would be better but this does the job giving the least power consumed. I was surprised to see my inverter say 1,400 because I thought it was going to be a reduced power tank being so small. If it had the reduced 750 watt it would consume the same power but take twice as long so I wouldn't get the recovery advantage.

With all that being said, I'm very happy with it, and when I find that perfect 3-4 gallon WH I may just get it and gladly install this in the kitchen for the sink. It's so small I don't even have anything along the back of the cabinet because it's difficult to reach back there so plenty of room to mount it. And instant got water instead of 20-30+ seconds as it runs across the house. So as an under sink tank it should serve you well and take up little space; it could easily fit inside an 18-24" small bath cabinet.