I did my A2 telc long time ago with those guys:
https://academia-languages.ch/
it was quite cool, I went for exam with a friend and they did exam just for two of us
I did B1 (also quite some time ago) in Konstanz (yes, I know not Zurich - but it was half price!) in Humboldt institute and it was also ok (in a group of about 10-15 people)