I have the entire set of Oxford ATPL books to supplement the material from my actual training provider - Bristol GS.
Yes, the books are very good, and contain superb illustrations, but I would say that they tend to drop down into much more detail than is actually required to become "exam ready" especially if you are on a tight timescale. Sometimes this is beneficial of course, but speaking from experience of tackling a subject using both Oxford and BGS material, much quicker progress is made with the latter. You don't actually need to remember who invented x, why they invented it, and how it evolved to become y (for example).
The specimen questions in the Oxford books are very useful though - in my experience are harder than the actual exams questions: train hard, fight easy! (disclaimer: I base that comment on the BGS question bank - I sit my first exams in 6 weeks).
So, yes they are great books. But be careful to identify what you need to learn or remember out of them.
Hope that helps!