Giving blood is a good thing to do. It takes about an hour, end to end, and you’re asked to donate a few times a year. Not a big time investment, plus you get a free bag of crisps and cup of tea each time you do it.
It looks like it’s going to hurt, but it doesn’t, really. The needle feels smaller than it looks, so look away when it goes in. The discomfort is momentary – it feels like a prick from a thorn.
15 or so minutes later, you’re done. Just make sure you drink plenty of water before you go (otherwise they might not be able to get enough out and you’ll have wasted everyone’s time, not that I’d ever be that stupid, oh no), and more once you get home.
If you can donate, please consider doing so.