This 14kW, 240Volt point of use heater is a quality unit. I would rate equally with more established brands in the water heating appliance industry. I am impressed with the build quality. I would expect it to run for many years without much maintenance and even with daily use.
This may or may not be a DIY project depending on your plumbing and electrical skills. As a lifelong 2nd generation home builder & remodeler I would rate it as an intermediate to advanced level to install. It does require a dedicated double pole 240 Volt breaker and 6 gauge wire to be run. You will also want to run some HTTN as a grounding wire to the case for safety. This will require you to get inside your electrical load center (breaker box) to perform connections. If you are not familiar or experienced with this kind of work I would highly recommend a licensed electrician perform this. The 6 gauge wire is thick and requires some effort to bend and pull thru crawlspaces, attics or basements and in walls. The plumbing side of it is probably a little easier for most. The 1/2" NPT connections are pretty straight forward. You will need to tap into an existing plumbing system or run a new cold water line to this unit as well as the plumbing fixture. And then the hot out of this unit to the plumbing fixture. You may or may not need a professional plumber on this, but the tools for running PEX, copper or other may or may not be easily available to you. I guess it all depends on your exact situation. I wouldn't describe this as a quick and easy project that will only take an hour or 2. Unless this tankless heater is really close to your electrical panel and water is conveniently available too, and the fixture your supplying the hot water too is easy to access, then I would expect a good part of a day to install, even for professionals. There will be lots of parts, pieces, fitting and such that will be needed to complete the install. Planning will take at least 30 mins too. You will need to come up with a materials list, make measurements for the length of pipe and wire you will need, and double check all that before going out to purchase said materials. You will likely spend at least 2 hours on the electrical and another 2 hours on the plumbing. You will need to connect it up to your plumbing fixture unless you are tapping into an existing hot water line. Then you will likely still need to shut off the water to your house, drain down the lines and then cut and make the T connection and/or cap off a line. For a DIY first time, I would personally allocate a weekend to get it done. Of course it all depends on the situation and factors such as distance, accessibility, availability of 2 empty spaces in your breaker box (load center) and such. Again, this appliance really is an intermediate to advanced level of skill and knowledge to install.
After having stressed all that I digress back to the Airtheral product itself. It is nice unit. Depending on your source water temperature this should be able to handle a faucet and shower for most people during the summer months. During the winter and if in a colder climate then the flow rate will need to be decreased to allow the unit to overcome the greater temperature differential between the incoming water and the set output temperature. This 14Kw unit can likely handle a bathroom or kitchen faucet pretty much anywhere in the USA. In the South it will likely also handle a shower as well. You can go over there charts in the stock photos to see what your location is rated to handle.
Overall this one gets 5 stars from me. I have been using some Airthereal Ozone generators for years and I really like the company and it products.