I did it, did a couple styros. I would avoid going near the wrist area because you can see the vein through your hand and down your forearm if you really look. I stopped around the middle of the forearm and didn't really go near the wrist area. Funny thing, I actually looked up the vascular system of the arms just so I know where the veins are arteries were so I didn't cut them on accident.
Preface by saying I'm not a healthcare worker but from the research I gathered, the only thing you should be concerned about regarding blood vessels are "superficial veins". These are veins close to the surface of the skin, I think around the beans layer or maybe even styro(idk). You don't have to worry about hittng a major artery or vein in the forearm because they are usually pretty deep, as long as you don't be cutting around the wrist area. You know how to check your pulse, right? 2 fingers on the neck or wrist? Yeah, don't cut there unless you wanna lose ur hands. Major Superficial Veins run along the pinky side and the thumb side of the forearm, so as long as you do not cut on the sides of ur forearm and don't cut near the wrist u should be good. IDK about tendons and nerves though
bro fuck me im acting like i know shit XD i just chatgpt this stuff
Tl;dr: Don't cut on the sides of your forearm or near your wrist.