I just did so for the first time today. Oddly, I didn’t feel any effects (aside from the needle puncture). I was really worried I’d feel terrible, or that I might even vomit (I asked what to do in such case beforehand), but thankfully nothing. (I mean, I am underweight, just OK enough for the limits)
I only got a bit freaked out when I removed the bandage and it took my dumb ass a while to realize that the extra drop of fresh blood is too light (I probably peeled off the scab). Anyway, so I just put a band-aid over it. At least I didn’t have a white shirt.

I am just disappointed that I got A+. I mean, this isn’t school, I hoped for 0-. 😕 Well, searching the internet, it seems it may be good for plasma or platelets, but I kinda fear the machine xD

Anyway, the personnel was really nice, so that was quite helpful too.