That's a great toy!. No, it won't encourage aggression, but it will help wear him out. Actually, if he starts attacking your hands or feet, this would be a great way to redirect his energy.
It's a GREAT toy. I got a similar one (a tiger) for my former cat, and she loved to attack it; it didn't make her the least bit aggressive (except with the tiger).
It's a wonderful toy. Cats always attack something, wether it's a feather, a peice of yarn or a stuffed animal. Just make sure you don't let her attack your hands, and when she does redirect her attacking towards this toy. She needs to know that hands are not toys.
My kitties have a pair of rolled up athletic socks they've been hunting for months. No matter where I throw them in the house, they magically "appear" by my bedroom door a few hours latter. Tattered. Clawed. Bitten. They kill those socks over and over and bring 'em to show daddy.
Looks like a great toy! My JuneBug loves my Kitty stuffed animal that i have had since i was 4, it has a rattle in it and causes her to go crazy! But I tried getting her a replacement of another cat animal with a rattle and she will play with it but not as much lol.