Migros Klubschule courses typically have 10 to 12 people in a class, so you need to be pushy to get help from the instructor/teacher. Otherwise you will learn at the level of the lower half in the course or be left with the coursework to pursue on your own. That's my experience but I have none with ECAP.
If the course is meeting your (challenging) expectations, go with it.
I did an intensive to B1 level with ECAP in Zürich and have absolutely no complaints. The class sizes did tend to be on the large side - 15-20, but I do well in that kind of environment. It may be different for you.
As with all language schools it does depend on who you have as a teacher.
i once did a german course A1 at ECAP and the truth be told, there are not good, too many students in a class and you find those dont-care attitude RAFF students who are there cos they r forced to!..why not try EB-zurich? serious students and very good teachers or if you are looking for flexibility, Alemania Deutsch Schule( albisrieden-platz) is a very good school, just did my B2 certificate..excellent, their prices are also very fair. good luck. Regina