Others specifically mentioned Kobo as an alternative. I did a high level pass over the ecosystem before choosing them as an alternative to the Amazon monopoly, they seem somewhat equivalent to Chrome vs Firefox:

- supported formats, for the Linux issue: EPUB, EPUB3, PDF, MOBI, JPEG, GIF, PNG, BMP, TIFF, TXT, HTML, RTF, CBZ, CBR

- no native linux client: not a deal breaker for me

- is the company behind Kobo credible, will it be around for a while: yes, its owned by a credible company, 13.4% e-reader market share, probably shrinking

- could it be sold? Possibly: https://goodereader.com/blog/electronic-readers/will-rakuten...

- is there an export path if they go under: its Adobe DRM, so assumably yes with their support

- does the store work?: Yes, the interface is reasonable if slow, I could find books on it and buy

- are prices comparable: no, Kindle is cheaper in some instances but there is a price match (I used it, it works)

- are the books I want on there: yes, ever one of the 5 or so books I looked at are listed on the store, newest version

- is the reader comparable to Kindle: yes, same settings I use on devices and laptop, fonts, brightness, clarity etc all comparable

One thing missing is 'X-Ray', which is neat but not essential technology Kindle has. Kobo has a book search that is ok, but not as good.