Flat storage

I was wondering if anyone has ever used one of these? If so, about how many posters fit in one?

https://www.gaylord.com/Preservation/Document-Preservation/Storage-Boxes/Gaylord-Archival%26%23174%3B-Blue-Grey-Barrier-Board-Drop-Front-One-Sheet-Poster-Box/p/HYB09244

Also would it be necessary to put a sheet of acid free paper between each or are they fine to just lay on top of each other?

I currently have about 200 posters (and growing) and have several posters rolled together in large carpet tubes and shipping tubes but I have heard this is not ideal for long term and it seems to be taking up a lot of space.

I think storing them flat would help with storage space but flat files are expensive as are baroques (which I have heard mixed things about).