Since so many more are printed and usually more available than all other formats, they're not as valuable, but I wouldn't say they're worthless. The chirashi are worth something to many folks, especially in Japan where it seems there are more collectors for them. There are some photos of really well done collages of chirashi, and I think a lot of folks could keep them in something like a scrapbook with movie tickets, etc., and especially with the much smaller homes in Japan, chirashi are much easier to store.
To your question, it seems like the vast majority of one side of chirashi artwork is printed in B2, and fairly often B1 formats. I've never gotten clear answers on numbers, percentages, etc. of different formats, so I'm not sure who would know the specifics.
Here's a good article from JPoster.net about chirashi aka B5:
https://www.jposter.net/main/about-chirashi.aspAs JPoster.net said, the only time chirashi are available is when they're in the theaters while the movies are showing. The distribution companies probably require the theaters to return any that haven't been picked up by moviegoers, after the movies are no longer showing, kinda similar to B1s as discussed in this thread:
From: MoviePoster Collectors [mailto:moviepostercollectors@gmail.com]
Sent: Sunday, September 02, 2018 6:43 AM
To: Hideyuki Takizawa
Subject: Re: Dear Mel, Japanese Movie Posters
Hello, I have some questions:
Why are B1 posters less popular in Japan than B2s?
Do studios print and distribute equal numbers of B1 and B2 posters to theaters?
Thanks
****
Top Japan MP dealer:
https://www.ebay.com/usr/movieposter-japan%21
Sep 2, 2018, at 6:58 PM, Hideyuki Takizawa <movieposterjapan@power.odn.ne.jp> wrote:
Regarding the B1 posters, they are tightly managed by the film distribution company.
Since the theaters must promptly return the B1 posters to the film distribution company after the movie is released,
these B1 posters will hardly be distributed to the general market.
Thanks.