I don't really care about the border aspect, I don't travel to the states to race. When I do, it'll be as an extra car no equipment in someone else's trailer.
From a safety perspective, my tank is not out of date, and I know that they hydrostatic test them to much higher pressures. The cost? Not much really. Convenient to have a great use for my old scuba tank. I don't dive enough any more to bother with keeping my tank up to date now, so if I can find a new use for it I'm all for it.
As for whether or not to use nitrogen... I'm suspecting that half the stated benefits for nitrogen is all horse puckies, but it is innocuous enough that if I can get a tank real cheap it wont hurt.
Helium.... hmmm. It would reduce unsprung weight a bit, but does it react with rubber, will it bleed through rubber, how safe is it to use?
I don't think I'll bother trying it, but...
