Seems nice to me. The users hand is already likely to be over the key that was used to activate the pie menu, so this serves as a quick way to dismiss the pie menu again, or to activate the pie item.

Please note that this small diff has been cleaned up from its originally intention (testing) to something I hope is more efficiently reviewable.

I considered adding logic to work around in-pie shortcut overlap with pie-callup shortcut but this would be rare ( very few pie shortcuts use a non-modified alpha key) and the user would still be able to use numeric shortcuts. If it is an issue this behavior can now be turned off in prefs. In addition I plan to look into automatically removing underlines from pie items to avoid any possibility of confusion.

ALSO:

I was hoping to experiment with the following pie behavior (but I've run short of time lately... hopefully soon).
Has anyone tried multiple pie taps to select items from the pie. i.e. three taps to open then choose second item ( could try ignoring mouse movement at successive taps)? This would be handy for newcomers and wouldn't get in the way of power users.