The difference is huge. I forgot to mention that the clarity of the text is worse too. Even the guy from e-ink says you can't put anything in front of the screen without degrading the quality of the text. The same goes for those lighted screens (such as on the new Nook) via an extra layer, they state it has a built in "anti-glare" screen but in reality that is the compulsory layer added to light the screen, but the clarity of the text will be worse. Do not buy any ereader with a glowing screen or any reader with an extra layer on top of the e-ink screen.
Answer to a better e-ink text experience is for e-ink to get their act together and improve the contrast of the basic screen. I don't see people reading books with a layer of plastic across the screen. It's just common sense. But if you want to pay for that then that's your choice. As long as you know.
That photo you linked to has a ton of light on the screen, You have to see the screen for yourself in a lower light situation. Practically any e-ink screen is acceptable in bright light, not everyone lives in California. There's a massive problem with the contrast of e-ink but improvements are slow. Another display technology could overtake it if they're not careful.
It seems the English speaking world reviewers have missed the contrast issue. Check out this review from Bookeen's native France (via Google translate), it mentions the screen contrast issue as a negative. (There are other reviewers who agree):
I returned my Odyssey for a refund before the USB port snapped off (Design error no. 3 I guess). Still, at least there was no diamond pattern on the touch screen I had, they must have changed it. Better to get rid of it completely though. Only person who would be satisfied is someone who had not seen a Pearl screen without a "filter" in front of it.