I don't think there is any con other than expense of refills. But remember, no gas is completely temperature "resistant". Nitrogen may not expand and contract at ambient temperatures as much as air (mix of Nitrogen, Oxygen, Hydrogen {water humidity}, etc.) but there still will be a small effect. Since air is mostly nitrogen anyway, you really are only gaining between 0 and 20% at best. Is it worth it? It would be cool to tell people your tires are filled with Nitrogen though!