That is some mouth gag. If you get one, please report back about how it worked out. My concern would be that it could be painful enough to kill the headspace.
Are you referring to the Paul Scott gag or the silentium from MEO that nysubjack posted about?
The Scott actually looks reasonably comfortable. I think any pain would come from the position you could be forced to hold.
The description of the silentium says the bars are textured and it grips the lips and tongue very well. (So it doesn't need to be cranked down hard). My only concern would be the weight and if the pull on your tongue and lips would get painful.
The silentium certainly looks like it might be extremely effective if nothing else!
