Being a certified installer I can only say they stand behind their product, they can't control people that buy them online and have no clue how to install them properly, that said they won't take responsibility for poor craftsmanship of a bad install. Just like any and all equipment, it can only be as good as the installers you choose to work with.
Purchased new home with this system installed. Love the recirculating system. Quick to all faucets and efficient. The dishwasher and two different showers can be used at the same time and no cold shots. I also added a WiFi plug so my system is on a schedule and off when we don't need the hot water. Our friends have a different tankless system and it doesn't have the recirculating system. They say it takes a long time to get hot water. This is a great unit.
Stopped working completely. Homeworks plumbing has made 3 visits installed 5 parts under warranty and overcharged us. Still not providing hot water at anything over 2.4 GALLONS/minute. Mfg service will only help certified installers. Cannot recommend this Navien brand tankless heater. Probably will cut my losses and replace with different brand.
I have had an NPE-240A for 3 years. It has worked flawlessly. We are happy with it.