It's got nowt to do with handling.
Nitrogen is formed by distilling liquid air at -196C, Nitrogen also contains a few % noble(inert) gasses such as krypton, neon, argon, xenon.
The reason why nitrogen is used is it doesn't react to the heat produced by the tyres friction with the road, so maintains the pressure more accurately, ordinary "air" expands with heat, owing to the hydrogen content, a fact exploited by the germans with thier heavy water explosives, where H2O became 3H2O.
Obviously they will be better when cold or extremely hot than normal air filled tyres, but tyre temps remain fairly stable in use so if correctly inflated will be just as good.
Adding ULTRASEAL acts as a cooling agent, owing to its' high aqueous(water) content, it also stops 100% of punctures for holes up to 8mm, makes the tyres last around 30% longer, use this myself, a puncture fix is remove the screw nail etc and drive, is permanent cure, is totally non toxic, you can eat it, will make you sick but not ill, can be washed out with water, gives off no fumes.
tabetha