I am 6'3 and 205 with larger arms. These fit me OK. They run about 2/3 of the way up my arm and the top can be hidden by a shirt sleeve. They are 92% nylon and 8% spandex. They have a bit of ruuberband around the upper arm piece to hold it in place. The material feels like a women's nylon sock and I would guess holds up well to being stretched but not to snags or sharp objects.
Half sleeves are usually just a pit stop on the road to getting a full sleeve. You miss the smell of the ink and vaseline and crave the feel of the needle creating a masterpiece on your skin. People often start with a half sleeve before they decide to complete it and finish the entire thing. They are sometimes viewed as incomplete until the rest of the arm is done. They are easier to cover and you don’t necessarily need a long sleeved shirt to cover them.