Almost all the EInk readers are Linux-based.
The EZ Reader Basic (Hanlin V3) can run the OpenInkPot firmware, which is completely OpenSource (
release candidate 0.2-rc1). OpenInkPot does not support DRM-ridden ebooks, but it otherwise a improvement on the original Jinke firmware. If you do try OpenInkPot, its big advantage is a wide range of user selected options for how ebook text is displayed. However, this means that you have to actually setup the device to your liking (don't just take the default setup).
Overall, I would characterize the EZ Reader (Hanlin) line as good middle of the road no-frills ebook readers. Their primary advantages over other readers is their outstanding battery life (about 3 weeks), and support for a wide range of ebook formats. However, with the Jinke firmware, the level of support varies between ebook formats and I would say that it only really supports four formats well: FB2, MOBI, ePub and PDF. The last two using mobile Adobe Digital Editions, which is also now on several other EInk readers.
The 5" EZ Reader Pocket Pro is similar but newer design, with a few teething problems. It isn't supported yet by OpenInkPot, but future support is probable because Jinke does not lock down their firmware or use any binary-only device drivers.