I recently returned from one month in Mali, where I took the 1977 Collins guide to the birds of West Africa by Serle and Morel. That book could fit in my pocket, this book by Barlow is too wide.
I am new to birdwatching and am used to the Peterson guides with big pictures and pointers to fieldmarks and many illustrations for each species . This book crams 20 or so birds on each page, and puts all the illustrations up at front. It does give a few examples of male/female/immature differences, and it does show raptors overhead. In this it is better than the Collins guide. The pictures seem cartoonish though.
The text is quite helpful and I guess the names of the birds are more up to date. I did not buy this book because I was going to Mali, not Senegal or Gambia. But all of the 60 or so birds that I identified in Mali are also found in this book. The Collins guide did not give me enough help identifying the many small weavers I saw, so I used this Barlow book and my field notes when I returned to the US, and this Barlow book is clearly superior in this case at least.
The Collins book covers all the birds of West Africa, even though nearly half get less than 10 words and no picture. Still, it has to be my first choice for countries other than Gambia and Senegal, especially since it is more portable.