Just achieved the certification SAP Certified Application Associate - Procurement with SAP ERP 6.0 EhP7.
I did the Mini mock test for several times gathering my mistakes and then studying it on PDF materials to understand why I got the reply wrong. After I started getting a very high % on mini test, I went to the full test, and the score kept growing each time. Scheduled the exam, and done. Passed.
If you use the ErpPrep properly, study on daily basis and map your mistakes and understand why you marked the incorrect answer. It is a succes for sure.