I sometimes demonstrate the same to students on a 152. It makes interesting learning, especially when they see that in order to get the prop to windmill the speed needs to be in excess of 110kts. You need a LOT of height to demonstrate it safely. Of course using the starter motor makes it all happen a lot quicker.
Might make interesting reading in the AAIB report.. "I stopped a perfectly good engine to see what it was like, and the starter motor failed and I couldn't get enough speed to get the prop going again..."
------------------
"Take-off is optional, Landing is mandatory"