The one I saw set off the gun.
And as mentioned, I would expect it to go off from half cock, so I wouldn't rely on the finger in the middle technique.
I have the comp hammer and it has lots of traction that I use to dig into the meat of my thumb tip. It really can become a smooth motion with plenty of practice. But however, I wouldn't recommend this set up for pure novices...(someone has to buy glocks - sorry haven't had much coffee this am.)
I also like to let the RO know I'm decocking if they haven't RO'd me before...just to let them know - that I know what is going on...probably not needed but it makes me feel better and puts my brain in "super attention mode" too.
ymmv