First off, GadgetsGo has the best price on the the Navien NPE-240A, hands down. I ordered my tankless on a Thursday, paid $30 extra to rush it to me and it was at my home the very next day.
The Navien NPE-240A performs flawlessly. It supplies plenty of hot water throughout my home.
The only problem I have it that it's mounted on a wall in my garage which is next to my room. I definitely hear the recirculating pump coming on every 30 minutes to make sure there's hot water going to all the faucets. It's makes a slight hum but nothing that's unbearable.
This is an excellent option, even for a larger family like ours. We have 6 people in a 3,400 sq ft home. The house is busy. Thiis water heater took me a day to install, counting removal of the old one, changing out plumbing and a trip to the hardware store. We are very pleased with the performance, and are confident in the cost savings now that we no longer are keeping 50 gallons of water hot 24/7. The temperature rise is 95 degrees, and the flow is still just fine.
Advantages: Cost, long term predicted reliability, reduced resource usage.
Disadvantages: Slightly longer delay (10-15 seconds extra?) for the first shower, but we did not plumb in the recirculation to the shower, which is an option for the future if we so choose.