OAA ATPL theory DL question
 

I am interested in OAA ATPL theory by distance learning method after PPL training which I will start soon.
I am in kind of love with OAA's PPL CBTs set which will definitely be used with OAA's PPL text books. I do think their CBTs are great for studying support with clear explanations of the concepts.

Distance Learning | Oxford Aviation Academy - OAA.com

I gave a look at this page and there's one thing I can't understand. I want to know whether I will receive CBTs too or only the text books?
What is Oxcel? Are its content the same as the CBTs ones? Or are they different???
Are the CBTs to be bought separately???

Thanks!