What would be a good test for this? Do you lose pressure?

I have a Rheem RTG-53PVN (made by Paloma) natural gas unit. It was put in about a year ago and I can't detect any difference in pressure one year later. I don't have any buildup around the shower heads, so I guess my water supply may not be very hard.

I paid about $670 for my unit and I was able to get $300 back in the form of a federal tax credit. That seemed like a total win until I realized the price of the 3" stainless steel exhaust pipe this particular model called for. The pipe actually ended up costing more than $700! Luckily, a friend and I were able to install the whole thing successfully ourselves.

The electronic temperature control on my unit is capped at 120ºF. There is a way to modify the controller to allow up to 140ºF in case you live in a high-altitude area. I was planning on doing that, but I find that 120ºF is WAY more than enough heat. I don't think I could stand more than a few seconds under that kind of heat.

The model I have is very quiet. You do hear some sort of motorized noise if you're showering in the room that has the heater on the other side of the wall. It's not very loud or annoying at all.

Overall, I think the tankless heater was one of the best things I've done to this house. Because I live alone, constantly heating about 50 gallons of water seemed very wasteful. Towards the end of the traditional heater's life, it was only good for about 10 minutes anyway.