Perhaps you would be better able to judge if you asked the students. The turnover in questions alone should give you some idea of how this site is rated by students and others all keen to learn more, whether specific or more general.
Then looking at the questions asked you will see the wide range of questions posed and how quickly they are answered.
Of course no site can replace the face to face aspect of learning; but it can do a lot and be a very valuable service.
- For Teachers