My first sprocket was changed at the first service, I was told there was a fault with it but no more detail. The sprocket in the video has done about 14000 miles and does show wear but not excessively so. The tension is set to a bit more than 45 degrees of twist on the top run and doesn't jump teeth. I would say that the belt noise is a bit exaggerated as I just used the built in microphone which of course was located in the same aluminium box as the belt and sprocket!
I'm with you on the lack of need to have two flanges on both sprockets and have seen the amount that the belt can move when aligned badly. By rights I really should repeat the video with the spindle deliberately misaligned to the left and to the right to demonstrate the way the belt can walk side to side.
With the alignment between the front and rear sprockets on the early cars (when they are actually aligned "correctly") I would expect a second flange on the rear sprocket would force the belt to bend between the sprockets which doesn't seem like a good arrangement.
