I studied "Waiting for Godot" for A-level English Literature, and bought this book not really knowing what to expect, thinking it would be more like a typical A-level exam revision guide. It wasn't. Rather, I think it is aimed at undergraduate students. It goes much deeper into literary analysis than is needed at A-level, while anyone at postgraduate level will probably have access to more extensive criticism such as in academic journals.
If you're expecting a B in English literature, this book is probably more than you need, and you may be better off studying the play more closely and using study guides and notes aimed at A-level students. If you're going for an A, it's worth spending a few quid and some time reading this (it's neither expensive nor particularly long). It will give you new ideas and a deeper understanding of the play, and could really help you to impress the examiners.
In my case, I think it helped me to get a high rather than a low A or a B for this exam, which was important as it brought up my English Literature grade overall. Even though (or probably because) it was aimed at a higher level than my exam, it gave me useful insights which really helped me in the exam.
I bought this thinking it would be both a critical guide and incldue the text of these 3 plays but it only contains the former. But well done Amazon - their returns section (Go to 'My Account') has a neat facility which prints out shipping labels etc and then refunds you the cost plus an estimate of the postage. Ok, you have to package it yourself and go to the post office but that's ok.