Last night I was thinking of idea's to simplify the gearing of a bike. I came up with a concept of a single adjustable gear. After thinking and doing a little research today I found this which appears to my cover my concept. Now my question has a design like this or the concept actually ever been implemented into any bikes (custom or otherwise). Are there flaws with the concept or that design in particular that I may be over looking? Also what do you think of the concept, assuming there was a design that could implement it well.