I love ONR.
It works well, and I would say that I've not induced any more marring with it than with traditional washes. Like anything, just use good technique and tools.
It saves a lot of time because you don't have to drag the hose out and put it away, etc. Plus you don't have to drag the hose around for rinsing, or have it on the ground to trip on.
One situation I used to have a lot before ONR was that my car would be just dirty enough that I'd like to wash it, but not dirty enough that I felt like dragging the hose out, etc. Not a problem with ONR. Just mix up a quick batch and wipe it down.
It saves on water since you only use what you mix up in the bucket.
I can wash in the sun if I have to or pull in my garage and wash there if I want to.
Since I'm washing one panel at a time, I can get interrupted (kids, wife, phone) and come back later.
It seems expensive at first glance, but you only use 1 oz of product to 2 gallons of water so it goes twice as far as traditional wash shampoos I've used, plus the water savings.
It's multi-use, you can mix it at different dilutions to use as a clay bar lube or quick detailer.
The only thing bad I can say about it is that I can't buy it locally. So, I try to buy it when Autogeek or another vendor is having a sale + free shipping event.
I generally don't use it on a REALLY dirty car either, but when I need to I can just stop by the local hand bay car wash, blow of the worst then ONR. I DO still keep some traditional shampoo on hand. Sometimes I just feel like doing a traditional wash
Give it a try!!