is the filling of nitrogen in the tyres good or just air?
It depends on if you want to pay for it considering the benefits. It is supposed to make an improvement in fuel economy of around 2%, needs to be re-filled less often than air, reduces the amount of water that can accumulate in your wheels, and reduces tire pressure changes as the tire temperature changes.
Yes the filling of nitrogen is worth the 20 bucks in my eyes. Nitrogen molliculs are almost twice the size of an air molicule. the larger size reduces your chances of slow leaks it doesn't expand as much while getting your tires hot from driving keeping your pressures more constant and that helps maximize fuel economy and road handling slightly.... hope that awnsers the question for ya