With monkey puzzle there are two challenges. The first is that the tree is a coniferous tree, and as such you have a marked difference of hardness in the annular rings. As the softer parts of those rings are very soft, you have to use really sharp tools to get a decent surface off the tool, because you can't do a lot of sanding (as that will just remove more of the soft parts and create ripples).
The second challenge are the knots. They extend from the outer edge almost right through to the centre. These knots are very hard, almost like a tropical hardwood. They will cut cleanly with a sharp tool, but good tool control is needed so the tool doesn't bounce around. They do make for very nice visual features, though, due to the strong contrast in colours.
