DAR
I would think for most aircraft the slight potential improvement in glide performance is not worth the gyrations required to get the prop to stop. In the event of an actual engine failure I think your energy should be going towards trying to get the engine running again. Once you are sure it will not produce usable power than the important thing is to concentrate on keeping the aircraft under control and managing the flight path so it touches down at the desired spot.
I tried the engine stopped trick in a C172 when I was a young instructor. To get the prop to stop I had to be in stalled condition and so there was an extra loss of altitude during the process, which IMO probably cancelled any gliding efficency gain. I also tried to get the prop to windmill start. As I recall even quite high airspeeds (130 kts + I think) would not budge the prop, so I restarted with the starter.
In any case the older I get the wider the yellow stripe down my back gets. I personally try to avoid deliberately creating emergency situations as in this case failure of the starter would require an actual (and entirely avoidable)force landing. This was not meant to imply you were reckless just that I have made a personal decision not to do something like this.
However for aircraft fitted with a variable pitch prop, going to full coarse results in a very usefull reduction in the gliding rate of descent