The Premium Exams were from my point of view a great buy.
By exercising 2 weeks before my SAP CO certification with these mock exams I am glad to say that I passed my certification exam with 96%. And the best part is that I felt really prepared and confident going in, which is largelly the result of being able to train with the questions and the time-dependant set-up. Even if I knew the theory well, it is great being able to see the wording and the context of the questions.
Highly recommend the premium exams for the CO module.