AFAIK, you can't then print the book or download as PDF. This used to work, but the WMF decidef to break it and never fixed it.

2022(e)ko api. 16(a) 11:43 erabiltzaileak hau idatzi du ("Amir E. Aharoni" <amir.aharoni@mail.huji.ac.il>):

Hi,

As far as I can see, the Collection extension, which provides the Special:Book page, is deployed on nearly all Wikimedia wikis.

Is there data that shows how often do people actually use it?

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Amir Elisha Aharoni · אָמִיר אֱלִישָׁע אַהֲרוֹנִי
http://aharoni.wordpress.com
‪“We're living in pieces,
I want to live in peace.” – T. Moore‬