I kinda think nitrogen is bogus. If someone would fill ya for free, I'd take it, but wouldn't pay for it.
I have it in my cage, haven't noticed a difference in my Hyundai.
Room air is 78% nitrogen. So does increasing the concentration 22% do any good? I really don't think so.
But N2 is bigger than O2 (21% room air) right? A nitrogen atom is 65 picometers. An oxygen atom is 60 picometers. Stick them together in their diatomic natural state and you get a nitrogen molecule approx 130 pico in diameter and an oxygen molecule about 120 pico in diameter. So the question is whether that 10 picos make a difference in air escaping from a tire? I just don't know if anything in a tire is exacting to 10 pico to make it worthwhile.
Compressed air from your local compressor will contain some moisture. Nitrogen, on the other hand, should not. This being said, the moisture in compressed air used to fill tires is one of the main culprits that cause deterioration... Oxygen is the other.