They are very cheap, it's more of a cooperative arrangement than a commercial school AFAIK.
In that case, it would really depend on the teacher. I did a few semesters of Russian there and I enjoyed it, but the class sizes were small and because I was doing the course in German, I was kind of learning two languages at once.
The way it works though is you can turn up for the first 2 classes and then decide whether to continue or not. Just do that and then you can check out the teacher and the other students. As usual for language classes, expect a fair amount of dropouts after the first 6 weeks or so.