Sony made some well-built eReaders. You could look at a used PRS-T2 or T3 (the T1 had some "teething issues" but was still usable). These three were based on Android. The PRS-350 (5"), PRS-650 (6") and PRS-950 (7") are based on Linux and are solid readers. None of these require registration and all come with the Oxford English Dictionary. These come up used on at Shop Goodwill (
www.shopgoodwill.com) and eBay all the time.