I am very happy with the teaching I have received from the Swiss French School and I feel that my level of French, particularly the grammatical structure, has improved significantly since I started my lessons. I was starting with a strong base so I cannot say what they are like for a complete beginner.
The best thing that I have found with the school is the quality of the teaching itself. The small class size (never more than 3, regularly just me) means you get plenty of time to discuss around the topics rather than just follow a rote timetable and the teachers are very friendly and approachable.
The workshops are also very helpful, albeit they are usually a lot busier, and the social events get rave reviews (although I have been unable to attend one myself.) If you book in advance, the flexibility around the lessons is also very helpful.
So, what stops it from getting five stars? Firstly, it is relatively expensive, so therefore would be expected to offer more than a cheaper alternative. The main other drawbacks for me are the quality of the on-line material is not quite there. I rarely felt like I was learning when completing a lot of these exercises and the system had some simple flaws. Finally, because the school is very busy, if you need to rearrange a class or re-take a level, then it can be very difficult to find a space in the immediate week or two, particularly if, like me, you were studying after work.
However, overall I was very happy and have continued with SFS to take me to my DELF exam in June, so I would definitely recommend them to anyone.