I have the equivelent made by Graupner that I bought when in Germany. From what I can tell, it's a lot better than the GP model. It has very solid, square fiberglass posts. I really like it and it's a lot more accurate than the two-finger method.

It's the sort of thing that would be easy to make if you have a drill press and a table saw using a good hardwood such as maple. The problem with Great Planes isn't the idea behind their tools (with some exceptions) but the implementation. The quality just isn't there which is unfortunate because they certainly have the marketing power and the money to do quality if they cared.