Do not buy any of these:
Or any other device that uses an eInk display.
I am also including this in the Do Not Buy list:
It uses a transflective non-backlit LCD display. But it’s no good, either.
I have seen what eBooks could and should be — and these devices are like an MITS Altair compared to today’s computers.
How many of you want to be stuck with that?
These devices are not good for eBooks, they do not represent anything other than a blind and ill-fated attempt to create an eBook market, and the more people buy these, the more they prevent true eBooks from emerging.
Using these devices is a vote for the past. Don’t head that way.
Save your money. Save your time. Save the frustration each of these devices will create as you wrestle with them.
You are not missing out on eBooks by not having these.
But those who have sunk their money into these and eBooks for them are at risk of missing out on eBooks.
Pity them.
The eBook Test 
What are your REASONS for saying they are bad. They all have room for improvement, but I am happy with mine (which is the second I have purchased).
That's all I can say. For now.
I take it that the future is flexible?
>>>I take it that the future is flexible?
If you mean in the physical sense of a roll-up screen, then no.
I think I agree with you! I have a Sony PRS 505 and it's very much a first generation device. I don't think that e-ink has a future. It's just too limited. Cheap, high quality, energy efficient LCD tablets are the future.
I agree the devices are limited. They also lack the "feel" of a real book.
However, they provide me quick access to multiple books with an adequate screen. They aren't perfect, but they are available on the market right now with enough material to be viable.
If/when a better evolutionary product appears, I'm sure all of us will flock to it.
So lemme get this straight. Don't buy anything because you have seen some top secret classified information about future ebook screens that you cannot share and a year from now there will be something better on the market (shocker) so you're coming down from the mountain with a stone tablet and you expect people to go around bleating "four legs good, eInk bad" or something. Thanks a lot chief, now I want to purchase one ASAP even more :/
>>>Thanks a lot chief, now I want to purchase one ASAP even more :/
Hey, it's your money to waste.