If you make one small mistake, you get the whole thing wrong and it gets frustrating when you are working on a chapter you haven't learned. Owls basically forces you to learn the material. Can retake until perfect grade. They helped a lot when it came time to study. I did not like the way the problems were set up.
Owls are good.
They help study for tests. They are done. Sometimes the answers are wrong, and notation is too picky. The owls helps familiarize new material and give practice. Too particular with some of the answers.