Overall, I think this is a great product and I applaud the effort and time that went into creating it. I got it for my cat and have noticed 2 things that could be improved.
1. Cats don't always play with the bird head on, so when they are "upside down" and begin to attack the sleeve part, their sharp teeth pierce through the material relatively easily. She was also extra stimulated due to the Catnip, so that probably affected her aggression. That being said, I think the sleeve could do with a layer of quilted fabric for more protection.
2. My cat seems to want to sink her teeth into the toy, but because it's built like a stuffed animal, it's hard for her to get a good murderous grip on it. It's a little large for smaller cats to adequately maul if they want to get their mouth on it.
Overall, I think it is a good purchase. I just think it could do with a bit of tweaking specifically for cats.