Helpful and, at the same time, not helpful (in a non-paradoxical way). Allow me to explain, starting with how it is not helpful. The book contains what I would call some counter-productive ecumenicism between the apologetic methodologies. As the title indicates, the book is supposed to contain five views (classical, evidential, cumulative case, presuppositional, and reformed-epistemology) on apologetic methodology, thus one expects there to be meaningful contrasts drawn between the different views by the authors who respectively hold to the different views. However, some of the authors stress Christian unity to such an extent that it becomes unclear what is unique about the specific methodology that they represent. For example, I still have little idea what makes Feinberg's (cumulative case) methodology different from Habermas' (evidential). Craig (classical), while presenting a strong argument for Christian theism, also does a poor job differentiating his methodology from evidential apologetics. By contrast, Habermas, Frame (presuppositional), and Clark (reformed-epistemology) each present clear cases on the basics of their methodologies, with Habermas in my view successfully arguing by the end of the book that the two remaining methodologies are really in his camp. As a result, the book basically ends up with three views (classical/evidential/cumulative case, presuppositional, and reformed-epistemology).
This leads to how the book is helpful, as there is significant clash between these three views. Frame and Habermas in particular have several productive interactions on Biblical epistemology, neutrality in argumentation, the use of evidences, and circular reasoning (with regard to one's standard of truth). I think Frame comes out on top on most of these issues, but Habermas makes a good point that, for all the talk of how presuppositionalists are fine with evidences (but not evidentialism), there has been little to no scholarship presenting Christian evidences from a presuppositional perspective, something that in my view would be quite useful. Clark's reformed-epistemology is interesting from an intellectual standpoint, but it appears dangerous from a Biblical standpoint. Scripture says that God's "invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they [those who refuse to worship God] are without excuse." (Romans 1:20). But Clark denies that there is any apologetic that can show Christianity (or theism more generally) to be rationally compelling or even just probably true. This leads him to say that atheists can be entirely rationally justified in rejecting a belief in God. To say the least, this does not leave unbelievers "without excuse," quite the opposite in fact. Most of the other authors do a good job rightly critiquing this as far below what a Christian apologetic should do. Frame's presuppositional apologetic is the best of the presented methodologies and has the added benefit (compared to other presuppositional cases) of not completely throwing 1000 years of Christian apologetics out the window. Frame is gracious and relentlessly Biblical in his argumentation, pushing all apologists to stay true to what the Bible says about truth and God's authority. I am pleased that all the authors of the book reject the idea that an apologist should feign neutrality. We should not pretend to be neutral about whether Christianity is true in order to show why one should become a Christian, because no one, Christian or non-Christian, can be neutral towards the Truth of Scripture. Additionally, all of the authors conducted themselves with the charity that brothers in Christ should have towards one another. The humor of several of the authors (especially Clark) is welcome as well in a book with so much philosophy. While this book certainly has some missed opportunities, it still presents a useful comparison of apologetic methodologies without dumbing down the philosophical language (at least not too much).