Aware of a few of those myself --- one (I thankfully did not witness) of which was only "successful" after several hours. During that time the individual was found by loved ones (if I recall correctly) and taken to the hospital. However, there wasn't much the medical staff could do given he'd pretty much removed the entire front of his head.
So should a person truly chose to end their life it would seem to be worthwhile to understand enough biology/anatomy to make it a quick transition - even if only for the sake of those that will be left behind.
Of course that's reminding me of a suicide intervention course I once took where the instructor (who worked as an operator/trainer on a suicide hotline) told a story of one of her former employee's first (and last) day on the job. If I recall correctly the young lady had showed up for work and one of the very first calls she received was a caller who called in saying someone was about to commit suicide. When she started to engage by trying to get additional information the only thing she heard in reply was a firearm going off.
Obviously not the most pleasant of stories, but given the topic they're probably ones worth sharing.
Personally, I'm not all that concerned with when/how I go I given I could/should probably dead many times over already ...... in fact at this point I'm almost more terrified of not dying than I am of dying, but I figure if I continue to live life it'll all get sorted out it's own time.