OK, thanks for your answers.

I'have been in a shop to try the NGS and Wacom. At the end of the day I decided for Wacom, first because the NGS pen was so weak that the demonstration one was half broken, and second the "touch" on the surface wasn't at all the same, and Wacom was hundreds times better than NGS. It's more than better, it's a pleasure to draw on wacom and comparatively you have the feeling to struggle on the NGS.

So, obviously it worth 100 Euros more. It' a long time investment (much longer than a PC...).

Qasar