[dredmorbius]

DJVU is supported by numerous book-reading applications, including (in my experience) FB Reader (FS/OSS), Pocketbook, and Onyx's Neoreader.

As a format for preserving full native scan views (large, but often strongly preferable for visually-significant works or preserving original typesetting / typography), DJVU is highly useful.

I do wish that it were more widely supported by both toolchains and readers. That will come in time, I suspect.