Alaric.us: I would venture a guess that violent means are more successful than others. Shooting oneself in the head or stepping off a tall building are both fairly definitive it seems.
To solve the mystery here, the most effective way of killing yourself is a shotgun to the head. Other methods involving guns may not be as effective, but still rank fairly low on the agony and time to death scale. Four methods involving guns feature in the top 8. Your suggested method, jumping from great height, ranks 7th with a mere 93.4% lethality. Yet it also ranks higher in the pain scale than most gun suicides - and at almost 5 mean minutes for death to occur after impact, I find it to be quite a shit way to kill yourself, honestly (not that killing yourself isn't shit anyway).
(I'm not making fun of suicide, by the way. One of my former classmates did kill himself by jumping from a skyscraper, while on vacation. Definitely a mental illness related suicide, we're thinking some form of impostor syndrome, but we'll never know)
Alaric.us: Still, just because something is a good tool for killing oneself doesn't mean that it should be forbidden to all.
That is correct. If the tool is manufactured with the sole purpose to kill as many human beings in as little time as possible however, then it should be forbidden to all.