Both have value. Ed's book is a must have and IMO goes deeper than Dummies, however, Dummies will get you started with how to hold the monster, how to tune it, the basic dirt simple stuff you need to know.
I use the patterns I found in Dummies to this day. So, I recommend you buy both and start with Dummies, but, I also recommend you be looking at Ed's book before completing Dummies. Ed's book gave me scale degree numbers, i.e. R-5-8-5 and that helped me understand what notes, and why those notes could be use in a bass line. Ed has a knack for putting words together so we understand what he is saying.
So --- get both and work from both.