I have the PRS-505 and I also bought the official light-cover case... it's really nice, though a bit heavy. It's bright enough even on the low setting... though I used a black permanent to lower the peripheral light problem caused by the light-wedge.
The cost of the PRS-505 and cover together is the same as the PRS-700 but I went with the 505 because I heard the readability is better (due to the 700's touchscreen). And I am very happy with the red aluminum casing (the 700 is plastic).
But of course the Sony Readers (and everything except the Iliads) are crap for technical documents.
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