I'm obsessed with tea pets too.
The Qilin and Pixiu are quite different creatures. Their appearances are supposed to be quite different as well, although they sometimes do resemble each other. The biggest difference is that the Pixiu has a big belly.
According to legend, the Pixiu was an evil creature who ate people and livestock. The king of heaven punished him by only allowing him to eat gold and sealing up his butt so he could not do his doody. So in Chinese culture having a statue of a Pixiu is considered lucky and will help bring gold into a home or business, but will not let it leave.
The Qilin is a benevolant creature who, it says, will not even harm grass when walking on it. It protects the good and is quite vicious when encountering an evil person. Statues of it are supposed to protect the innocent.
Both animals are a mix of other animal parts including dragons, deer, fish, etc and that is why their heads sometimes look similar and are hard to tell apart.