He knows this and that's why I'm pretty certain he wouldn't buy them used. Basically, he's thinking convert to standard, or see if the air ride system for another car will work (well, that was my idea. Apparently not a good one, ha ha).
He's hesitant because he's always had new cars so he just replaces whatever's needed with the exact thing that came off. In this case, its an old car and there's a huge price difference between the air one and the standard one. He just doesn't want to compromise the ride quality by converting. I will let him know that actual people have said it's a good system. At this point all he's seen are testimonials on manufacturer's websites. Having real feedback willmake it easier for him to pull the trigger.