I just installed a cheap N900 digitizer I've bought on ebay, and it's now obvious that the quality of these non OEM parts varies.

Compared to the original one, this digitizer feels less solid (the plastic is thinner and it bends when you press a point in the center of the screen), the the touch is now much less sensitive so you have to press a lot more and it often doesn't register a touch.
The overall feeling is also quite rough when I slide with my thumb so I imagine that the coating material on the outside is different from the original.
Polarizer filter definitely is not present as well, the digitizer looks transparent and not dark like the original one. Maybe now without the filter the contrast of the screen is lower in this situation that's the last problem.
The speaker was also missing and I have to move it from the old original digitizer.

I'm going to order another one from the ebay seller you suggested and I'll let you know.
Let's keep this thread updated, our N900 are very precious but with the passing of the time they are getting older and the digitizer is one part that often needs to be replaced.

P.S: by the way, do you guys know a place where to get the Philips 00 size screws that are used on the N900 so I can change them before they broke? (apparently I haven't found them on ebay) Thanks!

EDIT: by the way, this is the digitizer I'm speaking about (bought around two/three months ago but installed just yesterday) : http://www.ebay.com/itm/Original-Tou...-/220809160699
Unfortunately I couldn't buy the one you suggested because the seller doesn't ship to Italy