I will tell you one thing. I just bought a 2000 LS400 and it has nitrogen in the tires and that thing averaged 28.3 mpg on a 400 mile interstate trip with a couple of some driving around in memphis (go to a mall) and in Jackson, MS (to eat and mail a package). I thought the nitrogen was BS (and still do). However, my wife informed me that the car got unexpectedly impressive fuel economy and it does have nitrogen in the tires. So consideration was given to buying a $999 nitrogen generator from harbor freight :chairshot:
After sleeping on it however, nitrogen in tires is just like those additives people put in their cars. It is snake oil. Makes impressive claims but no conclusive evidence showing any real world benefit. When the time comes to fill them back up, air is going in them unless the place I get the tires puts N2 in there for free.
FWIW, on the topic of snake oil.... My 94 LS400 was leaking coolant (adding a pint to quart a day) and I found a leak on the driver side but couldn't tell where it was coming from (drip every second or so; also had bubbles in coolant recovery tank and was worried about a blown headgasket). I put some Bar's leak from Wal-Mart in there (oily stuff with chunks and pellets in it). The leak totally stopped and the bubbles stopped. Car drove fine to Memphis without adding any coolant.