hah, yeah, I've just been reading about the magnets too and want them as well now 😅
It's an unknown to me wrt self-application. I have only had to self-inject a thing once, and that was a tiny needle into my stomach and that was fairly difficult.
I have no issues with needles applied to me by others for blood samples etc, I quite happily watch it being done. Got no issues with blood... I bleed a lot, because I'm a clutz who does a lot of active stuff, th worst case is I stuck a knife in my wrist and hit a radial artery once and was actively amused by the blood fountain. (This was very much an accident! Other people were somewhat less amused lol.)
I never really had any major self-harming habits, etc, so hard to know where that boundary lies in me.