Nitrogen vs. Oxygen

To point out something else: The way you fill a tire, it already is filled with atmospheric pressure(~15PSI) of Air(~78% N2 as stated) before you add which ever air you prefer. You can not vacuum fill a tire unless it has bead locks, because it would unseat the bead... so unless you are mounting/filling in a vacuum or a 100% N2 environment, your "N2 filled" tires could be up to ~94% N2 instead of 78%(Normal filled)... with some O2 still in your tire. So IMO, go for it if free, can't hurt. Not worth any extra money.