No idea how hard it is, but I did clinical trials in my college years for extra money (they were just testing generic versions of common drugs that were already out, so nothing too crazy) and we had to give blood every 15 minutes, then 30 minutes, then hourly, etc. so it was a ton of blood draws. I saw some people end up in serious pain by someone that didn’t know what they were doing, huge bruises all over their arms and lots of needles digging around trying to find a vein… not fun at all. I got lucky and had people that could literally hit the same hole every single time so I didn’t even feel it, but it could be pretty rough with the wrong person from what I saw. Everyone there had already gone through training so it wasn’t like they had never done it before, and some of them still had that much trouble.
I have recently switched to Optimale and although their more extensive tests say you need your sample drawn at a hospital or have a nurse visit, you can ask them for a finger prick test that you do yourself instead. The basic testosterone tests are finger prick by default. The reason they prefer a hospital visit for the more extensive tests is that you need to fill two tubes of blood rather than one for the smaller tests. This can result in guys squeezing their fingers too hard to get enough blood out to fill two tubes and this can damage the blood so it cannot be tested. The solution is to drink a lot of water an hour before you draw and to also put your hand in a sink full of hot water for five minutes before you draw. I then get a good flow of blood without having to squeeze my finger at all.
I’ve also tried to do them and quite frankly its a painful messy process that I don’t need in my life when you can get a full vial from a vein in the arm.