I am studying with Bristol but also bought a copy of the Oxford manuals from eBay, they are quite in depth and didn't see the point in buying the Bristol manuals if I already have all the information on the I pad. The other benefit is that sometimes a certain subject explained differently helps me to understand things more clearly.
I also tried contacting Oxford whilst choosing providers and they couldn't be less interested in me as a Modular student, whereas Bristol was straight back with any queries I had and have been since I started studying with them, its no accident they are so highly regarded. Also, I think the fact that your CV may say you "did your ATPL theory with Oxford" will make little to no difference.