I tried to use it a couple years ago, but ended up basically dropping it and never kept up with reviews. Personally, I didn't have time to keep up with all the reviews and felt like I wasn't covering enough ground. I thought it was nice to flag all the cards and just blitz through by topic sometimes simply to hit a lot of stuff fast, but that's about the extent of how I used it.
I found that PreTest and Lange Q&A had really good apps that i put on my phone and just banged through both for each rotation along with UWorld as I was able. That was basically the extent of my shelf prep aside from mandatory didactic stuff. It was more than enough for me, but everyone is different.
One of the most important things to learn in 3rd year is how to read question stems with a clinical focus rather than a basic science focus like you used for step 1. What this means is that you will focus on slightly different things in the vignettes than you're accustomed to, and the only way to get good at it is by doing a lot of questions. My basic approach was this (in case anyone finds it helpful):
1) Read last sentence of vignette - the actual question part
2) 2-second skim of answers just to know what I'm dealing with: lab tests, imaging, pulm diseases, blood pressure meds, etc.
3) Read vignette with an eye for answering the following two questions for almost every question:
----a) What is my working diagnosis?
----b) What is my assessment of this patient? (stable, unstable, etc.)
4) Make sure the above 2 questions are answered as much as possible before selecting an answer choice since the answers will strongly impact what you do
5) For diagnosis questions, your answer to the above is the answer, though they may use different wording (urge continence vs detrussor hyperactivity)
6) For next step/test questions, it's either a test to clarify 3(a), or something to deal with 3(b). Look for the thing you wish they included in the vignette.
7) Once you've selected a next step/test, ask yourself this question:
----a) what will I do AFTER I get my answer?
8) If you would do the same thing regardless of the result, pick another test (especially if the thing you would do is another test)
Obviously all that happens very fast, but that's basically how I approached shelf/CK questions. Frankly, I didn't think FC helped me much with that; time is probably better spent on doing as many test-like questions as possible. I loved FC for M1/M2, and my strong knowledge base from those years definitely made the rest of med school a breeze.
