[Django]-Using django-taggit, is it possible to limit the tags to pre approved values?

So you want a set of predefined tags and the Users as well as the TutoringSessions should relate to one or more of these tags. Thats (as far as I can see) what m2m-fields are made for.
Maybe taggit has some usability advantages (I’m not familiar with it), but the functionality described here can be achieved with simple m2m-fields.