Got cheapest capsules for silver .999 1 oz coins from China on eBay 4 years ago. No changes to the coins so far. I do spread some of those tiny silica gel packs around though.
I have no experience with the cheaper capsules, and I'm not even sure I know what you're referring to, but I have used air-tites for years and have never experienced a problem. If you have valuable coins, definitely don't risk putting them in untested or mysterious capsules. Find out who made them and make sure that they contain inert materials. You don't want to find out the hard way.
