This show gives you a great opportunity to get to know the characters a little better. The story follows the members of the 104th Trainee Squad during their trainingi, but Levi, Erwin and Hange make short appearences as well.
The art is just brilliant! Everyone looks super cute, even the head instructor Keith and the colossal titan.
Don't expect any deep story from this show though, because there is none. It's just a silly spin-off that will entertain you when you have nothing better to watch.