I used this unit to replace my old water heater. The volts matched the one I had replaced so I didn't need to rewire or add breakers.

The unit performed as rated in my south Florida home. For testing purposes, and because my incoming water is so warm in July (82.9F), I set the unit to 130F. The sink flow rate was 1.07 gpm passing through ~12 ft of pipe (6 plastic, 6 copper). The temperature increase was 39F (21.7C), from 82.9F to 122F. Assuming no heat losses, a 5.5kW unit should have delivered a 37.5F (20.8C) boost, about 1 degree F less than what I measured. But this difference is easily accounted for by the temperature drift. I have an old heat recovery unit on my AC. During the winter the incoming water will be around 10F lower, so that will be the practical test of the unit. But I still think it will serve my needs just fine.
Of course, with our hard water, I am concerned about scaling reducing the functional life span of the unit. The old tank water heaters can last up to 20 years. I'll be happy to get 5 years of service from this tankless unit.
I am very happy to have quickly replaced my failed water heater tank with this small tankless unit. It required no changes to my wiring, breakers, or piping. However, I do feel guilty about potentially adding to the peak load requirements of our regional utility. I have a 6.5 kW solar system on my roof, but only grid-tie. Hopefully, technology will drive down the cost of batteries in the coming years.

I'm excited to have this little unit. It adds 30--50F to the incoming water, which in our case comes from a solar hot water heater, bringing the groundwater (55F) up to 80--120F depending on the time of year. This unit just boosts that water a bit when needed.

Here was my experience with install:
I bought an ECO55. I installed the unit following the instructions. I turned on the water and the power. It functioned perfectly, except each threaded connection leaked one drop of water every minute. So I tightened the fittings a quarter turn more and the male fittings snapped loose! I contacted customer service and within two days had a replacement. I installed it with three turns of teflon tape and pipe dope (thread sealing compound) on the male threads. I tightened it up as much as I dared, holding the male threads near the unit with a needle-nose pliers and a pipe wrench on the fitting. It is now watertight and functioning as per spec.

I have installed three point-of-use heaters before and this is the first time that I have gotten a point-of-use water heater that did not have hex lugs on the connection point. If you look at the second photo (from a different brand), you will see how it has a place for a wrench to hold the male connection while the female connection is fitted. Instead of the force of the tightening being transmitted into the unit, it is held at the lug by a second wrench. This unit does not have this and therefore all the force is transmitted into the plastic of the unit, which is not strong enough. So please be very careful when tightening connections. I recommend using Sharkbite or other removable fittings in this situation. The extra cost is worth it when having to get a tight fit and potentially take it on and off. This would make it a four-star product, but their customer service was superb and I can't drop them down to a four-star.

What I wanted was a small point of use water heater that would not overheat the water. This product has met my expectations. My house hot water tank is about 40 (pipe)feet from the kitchen. It takes over 1 minute of running the hot water to get the hot water to the sink. I installed the heater in the riser hot water line of my kitchen sink faucet. IMPORTANT: USE ONLY A GFCI CIRCUIT BREAKER to power this device.

Now installed, it now takes about 2-3 seconds for the water to "start feeling warmer" and about 10-15 seconds to be at 110 degrees. More importantly, when the 130 degree house hot water finally reaches this unit, it will not overheat the water coming out the faucet. The hot water coming out your faucet will eventually be at your house hot water temperature. It's also important to know that the colder your input water, the lower the temperature will be AND/OR, the higher the water flow, the lower the temperature. Our winter cold water is about 65 degrees normally. This little unit can supply 107 degree water at full flow, within 30 seconds or so. Eventually, 120 degrees after about 1 minute at full flow.

It won't work miracles. If you have really cold water, don't expect the flow rate to be high to get warm water. You'll have to get a higher wattage unit. If your water is cold, you'll probably want to go with a small hot water tank instead of a tankless.

The unit will reduce it's power draw as the input water temperature increases. I've proved this with an ampmeter at the power panel. Initially, it draws about 23-25 amps, then reduces until no extra heating (power) is necessary.

Like all tankless hot water heaters, it suffers from the same drawbacks. A "trickle" of water will not activate the heating element and you'll have cold water gaps when used frequently. It is small and looks well built. It should fit under most kitchen sink cabinets. This was exactly what I wanted and so far, is working well. Again, ONLY USE A GFCI CIRCUIT BREAKER to power this unit.

I have used several of these for different rentals and they are always pretty good. I got a faulty one but the seller replaced it for me. Thank you!