you still have to wait for the revs to spin up, while im watching the rpms climb im working the clutch back and forth. I notice no difference in time. between true double clutching and the other thing. Besides, I usually am double clutching while heel and toe'ing for a turn, so I'm slowing down anyway.

By double clutching the layshaft is at the proper speed where when you hold the clutch in the layshaft is still spinning down from whatever gear you used to be in. As well as you are making your syncros work just as hard as if you had not double clutched at all because the layshaft goes from 3rd gear to 2nd gear without actually matching the speed of the engine. Lastly you would not be able to downshift a car with dead syncro's unless you double clutched properly.