If you're studying the Open University course A200 1400-1900 (From Medieval to Modern) then this book is a set book and you'll need it to complete the course. You'll rely heavily on the book throughout the earlier modules of the course, and an understanding of Wallace's views on the reformation(s) will hold you in good stead for the course final examination.
If you're not studying the course, then I'd suggest that you've got to be very interested in the period in question for this to be a must-have purchase. Wallace is clearly an expert on the period in question, however it's not an easy read for anyone other than a historian.