I didn't have a Blu-Ray player when these first came out, so I didn't bother buying them back then. Now I have one, though, and the other day I found these in a bin at Wal-Mart for about $8 each. Watched them both, one last night and one today, and enjoyed the new features, but mainly savored the excellent picture quality.
On the Labyrinth Picture-in-Picture commentaries, it seemed like they chose two people specifically because they appear in lots of Harry Potter documentaries: Warwick Davis and Nick Dudman.
Alex