If you are wanting a 5" format reader like the PRS300, I would suggest looking at the Pocketbook 360 instead. It's smaller, lighter and easier to handle.
http://www.pocketbookreader.com/PocketBook_360.html
And there is also a dedicated forum here on MR. The integrated cover is also a very nice feature. Their device has been selling in Ukraine for a while now and they are just ramping up US sales. In fact the contest MR is currently running will be giving away three (3) Pocketbook 360 supplied by Pocketbook.
In my opinion it might be the best quality 5" device currently on the market.
They also have an advantage in that their firmware is quite stable and developed in-house, not like other Hanlin 5" clone devices which seem to use the same firmware coded by the same developers across all the brands.
Of the people who have tried both the PRS300 and PB360, as far as I know all have preferred the 360. So you might want to read some of the threads in the forum here.