Pros
Clear data in terms of your student performance. Clarity regarding exactly what will be on the formative tests. All Mastery get-togethers. Great if you are a new teacher with a ton of time to commit and want to improve your basic instructional techniques.
Cons
Mastery is still expanding at a fast pace leaving little time to take seriously any innovation in regards to figuring out how to make their schools sustainable places of employment for adults who have families or want a dynamic life outside of their work days. Fast expansion also means that central leadership message becomes one of command and control rather than inquiry. Quick success seems to have created pressure NOT to change anything right now. If innovation is part of your motivation, then now is not the right time to work here.