Yesterday I gave my E_BW4HANA214 certification exam and scored 75%. Thanks to erpprep its really worth taking erpprep test before you give your real test. The questions are pretty similar to erpprep. But a through reading is required to score good percentage.
I recommend to go through Developing Hybrid Models with SAP HANA, Data Provisioning into SAP HANA and SAP BW/4HANA to get in-depth knowledge in overall concepts.