By the way, I bought the Hanvon pens N526 and N518 as well as the pen for the GraphicPal und Rollick Series. They all work fine with the Onyx Boox M92.
The only think one must be aware of is that the Hanvon pens need once screen calibration, because they point a few millimeters away from the original M92 pen. In general, I like the Hanvon ones much better. They have a more stable pen tip.
Unfortunately, the German Hanvon Shop closed just now. Is there any place where to purchase Hanvon pens?