The author of the Kaplan pharm section is one of the co-authors for the Katzung pharm book. The guy's name is Anthony Trevor and he lectures for Kaplan and writes their lecture notes for pharm. So, you aren't missing out, if you don't go for the "Katzung book" that everybody talks about. Same author, even more straight forward and condensed notes than the other examination and board review book.
Many students say that first aid alone is sufficient for pharm if your background is solid enough, so first aid + kaplan notes should be more than enough.
The thing you should keep in mind is that the majority of US med students don't prepare with Kaplan, so when you ask around most people will spout out the names of the authors recommended by first aid. Most of these books are good, and some are very strongly written, but some of the best review material out there is actually in the notes by the professional review companies, of which Kaplan is one.