Parkbremse,
From your post I understand that you are just about to complete your PPL.
If you are going to obtain your professional licences, you are going to need to pass your ATPL writtens. Now, when you enroll onto your ground school, you will be provided with a complete set of notes covering all 14 subjects. If that place is Oxford, then they will provide all your course material including the Jepp manuals. So either way, you will have all the material required to keep for future reference.
I did not do my ground school with Oxford, however, I did buy a couple of Jepp Manuals to supplement some of my notes (for a couple of subjects I found particularly hard), and I must admit they are very good. I can also recommend the Met CD they have on sale. It is an excellent tool for learning the Met ATPL syllabus.
Good luck with the rest of your PPL.