This is a good REVIEW book. Don't expect it to teach you or explain anything because that's not the purchase. It has great charts and tables that are well organized.
It is often referred to as "kaplan's version of first aid"
However, I have to say that it is better than first aid in how well it organizes information. Sometimes, though, it includes a little too much detail.
A combination of medessentials and first aid, in my opinion, is better than having just one.
If you had to pick 1, however, go with first aid. It's the gold standard.