A long time ago i did a lot of research on this issue. Can't find the article I did back then. Bottom line, if it's cheap, it is pretty much useless.

As a result of that research, I carried a Parat-C for years traveling until the TSA made it too too big of a PITA. The good ones are all sealed and all have expiration dates (which are probably worst case, but....)

Here's a later iteration of the article I did probably 10 years earlier. It's also old, but...

https://www.avweb.com/ownership/cockpit-smoke-hoods/