I was trying it out recently-even though I already didn't much like this method-and all that happened is me feeling my eyeballs start to bulge out of my skull. I'm having some eye issues and general face issues regardless so maybe that contributed. I am also pretty sure I was not doing it correctly as I did not follow a guide. But it still put me off hanging as an option for good. I wasn't even starting to lose oxygen (which feels bad enough), I just felt like one of those canine squeaker toys where the eyes pop out when you give them a good squeeze.
On the other hand, I talked to someone who ended up using that as their method (this was before I found this forum), and they did it with short notice when they knew they would be alone. They also did so while kneeling (I believe this is what is called "partial"?) so they had to consciously just lean all their weight against the rope, or whatever they had used (which I cannot recall).
I don't know how they overcame SI to that degree. That is complete loss of hope right there. They shared one of my own issues and that was what pushed them over the edge, it took away their ability to live, go to work, or even just enjoy the sunshine (which they loved). It was a swift demise. I only found out about it after the fact, when I talked with their spouse as they saw my email exchanges (& phone number) with the deceased.
I try to be vague about it if I ever bring it up as not to disrespect them or cross the sanctity of privacy too much, but even their spouse couldn't stop thinking of the manner in which they went out. When I imagine it, I just imagine the personification of giving up, just a kneeling body hunched over on the floor.
You mention young kids being successful, and some even by accident..I can't imagine any of them did partial. It must have been full. Reminds me of that story of that kid who tried to prank his family by making it look like he was hanging from a tree, only to end up actually hanging himself.