I suggest asking in the Kobo forums for more details about these readers...you'll get more answers from Kobo owners themselves rather than from owners of other devices touting theirs. I can't talk to the Glo which is being sold at Costco Canada for $127.99 with the Sleep Cover (usually $30) as a bonus but several threads in the Kobo forum give very detailed reviews about it.
I have a Mini: $80 in Canada.
- no ads
- very small and light (5" screen)
- several dictionaries available (select during set up)
- highlighting and notes available, I don't export so don't know if they can be exported
- fonts can be added without rooting
- screen is very good (IMO), fonts are crisp and dark
- I don't think a 5" screen is going to work with your pdf wish...pdfs are already not all that great to read on a 6" screen...
- you do need to register your device with a Kobo account in order to set it up but you can do that with a "dummy" account and never buy books or sync to Kobo after that
- shelves (collections)
- works very well with Calibre
- performance is fast
- no audio anything...
- no memory expansion
- can't change screen orientation
- touch screen (infrared)