$7 a tire at a tire dealer here in San Jose. Had it put into my Mercedes tires when replaced recently.
First time use for me, except when I was a Medic in the Army. We used "liquid" nitrogen to burn off warts, (using a long Q-tip) which is around 425dg below zero in the liquid form! We stored it in thermoses in the freezer.
I don't mind paying a little extra if it really does as claimed. But the jury's still out on this one. The darn tires on my car cost over 375 smackaroos each, so the longer they last, the happier I am. I do dislike the green caps...darn fugly.
As far a voiding a warranty? I believe the corporate dweeb doesn't have a clue that it is an inert gas and will not damage the tire. All nitrogen does is stay cooler than air with friction, helping reduce wear due to heat. Perhaps that's why they don't like it...
?
If challenged, they would not go to court on this one. I suggest fighting them if ever denied.