I think this would be more useful if the items looked realistic, and were not crude hand drawn graphics. If I want something hand drawn, I'll do it myself on a piece of paper.
the more crude your mockup is, the more the viewer focuses on layout rather than design. Crudity like this will keep people from saying, "what if we had rounded corners there?"
I think the look is excellent. It makes explicit to the client or whoever that this is a mock-up and not to be confused with the look and feel of the app/site. You can say that until you are blue in the face and quite often someone will say 'isn't that line a bit thick'.
Moreover sometimes designers can get locked into overly prescriptive design rough too early. This avoids that.
Another benefit of this app is you can easily share your work (I know you can scan your sketches). But a negative is you can't really interact with it or make comments (Balsamiq).