Minty, I will say you get what you pay for.... And Mark is a wise old Owl, I'm contemplating getting some of those myself. Though I guess it depends on how much you have paid for your posters, or how much they are worth now. There's NO way I would buy them for every poster I own anyway.
Most of my High end stuff is in Selwyns Sleeves, I have about 60 of those which take two posters. the rest are in plan chests with nothing between them; And many others which are still folded and in other drawers, because they have tape marks or some other damage I don't want my "clean" posters to come into contact with.
I will just say, if you are careful about light, and Temperature, these posters have lasted many years and are still in good nick, without our help. I don't think they are just going to fall apart over night...