i like this kind of cbt, sometimes i did it on myself, it's safe if it's done with hypodermic needles and taking a lot of precautions.
Testicles are very hard to skewer, so it's better receiving needles by a mistress or master, it's very exciting and it's intense phsicological experience.
There are people that inject fluids (like little percenteage of alchol or saline solutions...) in the scrotum, in the first skin layer or also directly in the testicle, but it's a little bit risky.