I've used this map many, many times and it is definitely the best map of the Peloponnese available. I will sometimes supplement it with the (higher analysis) maps also by Road Editions (the Achaia, Mani, Taigetos, Parnona, ones for example) but they aren't really necessary for general (driving) use. If you are hiking, this map is not specific enough, but if you are driving, this is definitely the way to go. The city maps are very useful (Korinthos, Patra, Kalamata, Nafplio).
You could plan a lovely trip just based on the green lines on the map (the scenic routes, as designated by the cartographers).
If you are going to the Peloponnese for tourism purposes, I recommend the Road Editions guide book to the Peloponnese also to go along with this map -- it's the best guide book available for this region and is available in Greek or English; easiest to get in Greece at any bookstore (although the Road Editions bookstore in Athens is worth a trip) or on amazon's UK site. The recommendations in the book are excellent.