Hi maverick3934,
Unfortunately there is no real way to know how long it may last because as you said there is no way to know what they are selling you or what the specs really are. You’ve probably read this but my thoughts about them are in post #2 here along with post #2 here.
There are some polyfoam sources listed in post #4 here. Check for foam types and prices because there is a wide range of both in the list. The first two probably have the best overall value (of the ones that list their prices online) but this may vary with foam type from outlet to outlet.
Phoenix