The Rotring 900 is an interesting pen. Here is a short but informative review of it.
I do not agree to the claim that it is different from other Rotring pens in that is not scratchy. I have yet to use a Rotring pen of any sort that is scratchy. To be sure, all of them are stiff, but that does not translate into scratchy in my experience.
It might also be interesting to point out that the Rotring Altro is a plastic copy or plastic "version" of the 900.