I think First Aid for Step 2 is a good book. I have not taken Step 2 yet, or really started studying much, but from flipping through First Aid it looks like a thorough and high yield book. I don't necessarily think that First Aid for Step 2 is any less valuable than for Step 1, but the difference is that many people don't have the time or interest in studying for Step 2 like they did Step 1. If most people spent 5-6 weeks preparing for Step 2, instead of 2-3 weeks, they would have more time to absorb what is in First Aid for Step 2. Plus, people here have proven that USMLEWorld is probably the best resource, coupled with another review book (many like Step 2 Secrets). Crush Step 2 is also popular, probably because it's a fairly easy read in comparison to First Aid for Step 2.
If you like the First Aid format, and want a good resource for Step 2, I would buy it and use it. If you prefer paragraph/textbook form, get Crush Step 2. If you like Q&A format, get Step 2 Secrets. You can also use a combination of the above. I plan on using First Aid for Step 2, just because I'm anal like than and really want to learn the material. I will probably also use Step 2 Secrets and of course USMLEWorld.