Back on subject, wow, don't overdo it.
https://youtu.be/puSK4XFHr8I?t=107
Jesus F***ing Christ oh god no. I gained a phobia today from that video.
I didn't like preacher curls, they were unnecessarily painful for little gain and I prefer free motion training anyway, this machine and bar crap is too targeted and look what it gets you. I did them only once and pulled a tendon enough that I had to PT my elbow for six weeks. I likely tore a tendon but only a little.
Seriously though, when I started working out my friend was really serious about it and said some very wise words to me:
1. Your tendons get stronger along with your muscles but you can get yourself in a situation where the muscle can be stronger than the tendon and well, you see the video. So always aim for at least 8 reps, 8-12 is best. You won't look like Arnie but you also won't get injured as easily.
2. Don't use steroids, see rule #1
Words to live by, RIP my friend.