>>16286471
>are they a good investment, or just doomsday junk
They're toys that can also be sorta useful depending on what you spend.
If you want to doomsday prep, you buy a really good MSA mask from Ebay and keep it and some top-tier filters sealed away in a box, and replace the filters every year. You'll spend hundreds on the initial setup alone.
If you want to LARP but also want something that will at least maybe sorta help in a disaster, get a surplus NATO gas mask. Israeli masks are generally ok, as is the German M65 (pic related), and the Czech masks are decently functional and look badass. The Czech masks have their own retarded proprietary filters, Israeli and German will use standard 40mm NATO filters. Depending on paranoia, you could buy new high-grade ones, or you could get old Israeli filters, which will be long expired but will still offer some token protection and be fine with particulate matter. Rubber degrades over time, so these masks won't fare that well against caustic chemicals, but neither will your skin for that matter. Avoid older filters when possible, even the ones without asbestos may contain hexavalent chromium, which is Very Bad for you.
Old USSR and Polish masks like the one you posted should only be used for larping, and you want a dummy filter. Virtually all of their filters contained asbestos. If the filter is damaged at all you're going to inhale it - and that damage may not be visible.