What solman said...
Nitrogen changes pressure less from heat or altitude than ordinary compressed air (because it is dry), which is why it's popular in planes and racers. Since it is dry, it will prolong the life of a tire that's on a vehicle long enough to make a difference, but if you wear tires out before they start to weather check, this doesn't really matter. It will also keep alluminum alloy wheels from corroding from the inside, but again, the difference is probably not worth the expense for most riders. Might be worthwhile on a show car/bike that is gonna wear the same tires for long periods.
$66au sounds like a lot of money. He's gonna keep the tires serviced for what, a year or less? I'd spend the money on something else.