They do? I always thought they were cheaper, I guess because of the very untrue hype of SP saying it is better than HP, or the fact that the company has to go outta it's way to fit a LP regulator on the tank instead of the standard HP regulator.
it can ultimately explode. especially if you get oil in the fill nipple. there's some nasty nasty stories and pictures of that happening.
To solve that, simply do not put any sort of oil or lubrication down, into, or around the fill nipple of a HPA tank. I'd also suggest that you get a fill nipple cover. they can be had for under $5 each
Now if you fill it yourself, make sure that you're not overfilling it or they can overpressurize and also blow up in the worst case scenario.