tuxor,
I probably read it one day earlier

It was "no longer in stock" then.
Beryll Snyder,
On a 9.7" screen left-right margins should be about 2 cm each, top-bottom - 3 cm each.
Although top-bottom is not as important.
With such margins you get the size of the text itself exactly like in a regular printed on paper book.
Furthermore, if margins are narrow, then on 9.7" screen the line of text is too long for comfortable reading: you have to follow the line along with the eyes and then to search for the beginning of the next line.
Long lines are not good. In the printed book business they know what line length is the best and they try to stick close to it.
So, with narrow margins, on 9.7" you would have to increase the font size to get shorter lines, but then you would have to read from a much greater distance - hands are too short for that.
I do not use 9.7" reader for pdfs with technical documentation: for that I have a PC.
I just want to have an experience of reading a real book, and therefore I need the size of the text on the page of a real book too. A 6" screen is not enough.
BTW, for pdf a different reader software may be invoked (as on PB902), and it may have different margin settings.
But work has to be done on a PC. Especially that 9.7" is too small for comfortably reading A4 size pdfs anyway.
An additional advantage of such wide margins is that you can use black reader instead of a white one.
With narrow margins, black frame very close to the text is bad for eyes, so only a white reader can be used - the plastic frame serves as an extension of the page, an additional margin. 6" or 5" reader always has to be white or light gray.
So, with wide margins you can buy a black reader and on a black reader the screen looks whiter which is very pleasant.
The rule is very simple:
9.7" reader - black reader, wide margins.
6" reader - white reader, narrow margins.
5" reader - buy a larger reader
I also like to have large top-bottom margins just to make the page be of the same size as in books. It contributes to the experience of reading "a real book".
A longer page is not too bad, less turning of pages.
Obviously, the best would be 8" reader. Where are way?
And finally, before I hacked my PB902 and installed FBReader180 on it,
I was not able to set wide margins. So I tortured myself with the narrow ones.
I can categorically say, that wide margins increase the pleasure and comfort of reading many many times. Like night and day.
If you are still using narrow margins, you don't know what you are missing!
(That applies only to 9.7" devices. On 6" there is no room for large margins, the text line is already a bit too short)
Booxtor,
As I explained above, I want wide margins and a black reader

So I will have to wait for the black one.
But meanwhile perhaps you can confirm if it is possible to set such wide margins with the current reader software? I don't want to buy a reader and then try to find a way to hack it to increase the size of the margins.
It is easy to do it on Kindle DX, but for left and right margins only, no top - bottom.
On PocketBook 902, it became possible only with FBReader180, not even with Cool Reader 3.
BTW, Pearl is darker than the old VizPlex (I have both), personally, I strongly prefer older eink screens.
So that makes it even more important to get a black reader, to get at least some psychological effect of a whiter screen.
Maybe I should investigate older versions of Onyx. I just like dimensions of M92.