Schumi,

You know that you don't need to use the clutch on a heel and toe downshift in a manual transmission, particularly a crash box.

With a synchro manual box a double de-clutch isn't even necessary. I do a single de-clutch on newer synchromesh units, if a synchro gearbox is going in for a rebuild I'll many times go clutchless

As for the blip on a Mercedes automatic, I can manually downshift my automatic where the engagement is imperceptible as compared to not using a blip on the same shift where the engagement of the downshift balks.

The only issue for me on blipping an automatic downshift on my car is that because of the pedal configuration left foot braking works best. I wear a size 10-1/2 or 11 shoe and no matter how I position myself I find the height and distance between the two pedals too far apart.