These thumb pick are shaped as normal guitar picks, but with a "tail" that attaches to the thumb. This is great for shifting quickly between finger picking and flat picking. Also great if you (like me) sometimes get so carried away on the stage that you loose grip of your pick and drop it on the floor... Not with these!
I find them too expensive, though. When I bought them, I paid 35¤ which is already a bit too much in my opinion. But now I see the price went up to 48¤, which I find quite unreasonable for bits of plastic.