First Aid is probably the most popular Step 2 CS book and it is very handy. It does need a thorough re-edit as it is littered with small errors that should be fixed. For example, case 17, William Jordan, states in the beginning he has less energy at work (a fatigue case) but later he states he is retired. Case 26, in response to alcohol use, Stephanie McCall says a couple of beers on the weekends and an occasional glass of wine with a romantic dinner and is asked the 4 CAGE questions. Not necessary. And in case 27, the challenging question of Rick Meyer, back pain sufferer, about having a couple of days off is answered "No - light duty." There is no light duty on construction sites. Give him a couple of days off and if he wants more, simply say "When the test results come back, we'll know if you need more time off." The US economy will not collapse if Mr. Meyer has a couple of days rest for his sore back.
That said, it is the most used and if you have a good partner or a good teacher, First Aid is very useful. What I like about it is the structure of the history: chief complaint, systems review, medical history and social history followed by a gateway question ("Do you have any food or drug allergies?") that will lead you to the PE.