I have thied clenching maybe two or three times, and it didn't work. Back then I thought I was doing it wrong, and after reading this thread I couldn't be more sure about it. The only pipe I can clench is MM Mini Ozark, which I smoke seldom if even then. :D
Otherwise, I'm afraid of either my teeth cracking or twisting, or, much worse, about leaving teethmarks on the stem. But maybe I digest the information you shared and give it a try. I would like to be able to clench, because, as pointed out here, sometimes it's at least practical.