There are some differences.

The Avistar is a decent airplane, just a little better than the Superstar 40. the Kadet LT-40 is sturdier and slower than the Hobbico models.

I have not seen the Alpha yet. (I expect I'll see one this year when helping beginners at the local field.) From what I have heard... it should be between the Kadet and the Superstar in durrability and flying speed.