The techniques they teach are more suited for tournament competition and may not be as appropriate for self defense. Typically, you'll find a strong emphasis on aerobic training in these schools. They tend to spend considerable more time developing strong defensive and offensive skill and my not place as much importance of rigorous physical training. Then, there are those rare schools that place nearly equal emphasis on both aspects. Attend class as a guest or visitor.
Most schools welcome visitors.
It gives the students a chance to demonstrate knowledge and training. Pay close attention to the instructors. Individual students respond differently to training techniques. Only you can determine what atmosphere would be best for you. Interview the Instructor.