I think there are at least two things, that make this alternative scribble app very valueable: at first we have xournal compatibility. That's awesome, since you can not only _add_ things to your existing scribbles on a computer, but also _edit_ what you scribbled on your M92.
But the other thing is: we now have some kind of sandbox to play with the general scribbling ability of the M92. Since we don't have source code access to Onyx' "official" scribbling app, we can't use that official one to try out things like implementing anti-aliased brushes, different colors, special drawing tools for straight lines, rectangles, circles, polygons or even complex paths, furthermore possibility to Undo/redo or maybe even pen pressure sensitivity. All this sounds really promising I think, since Onyx won't put too much effort into these things, that are not part of the concept of a "reader".