Back when I was in school, I used to print EVERYTHING on this stuff, because it's super super cheap and ridiculously easy to print on (no stretching, no bowing or warping, etc). I can't imagine really doing it for posters now that we're trying to sell stuff online...shipping individual ones flat sounds like a pain, and the idea of shipping a brick of those things to a band or whatever sounds like a pretty expensive endeavor. Those duders get heavy fast. And there's the not-archival thing, but I've got some prints on that stuff that are close to fifteen years old, and they look fine. As long as you understand that you're not printing a stack of heirlooms, you should be fine.
I use similar stuff a lot. about 2mm thick, makes very substantial, very tactile post cards and handbills. But Dan Black has a point, twenty posters seem like a stack of one hundred, so I mix the print run stock say 50 on 'normal' thin paper and 50 on chipboard, I only sell those in our gallery to people that pick them up right there, and the paper ones go places per post.
So Yeah, go for it!