When I was preparing for SAP HANA Certification and that time i was checking for a place where i can prepare and SAP Learning Hub was a great help .Whatever the books i want to refer and study then i have found those on SAP Learning Hub .It was really useful .Its online and really compatible. I have refer many books like
HA 250 .
The best part of it was that we get books as per certification code .So we need not to worry much about the contents.
So i would recommend everybody to go through SAP Learning Hub to prepare and prepare well for Exam .