Well I used it for my second review of FAR and have used Ninja MCQ exclusively for the past month. It says I've done 96 hours but this may be skewed because I leave my computer on with Ninja up when I'm not doing anything, so I'm not sure if that's how they count time or if it only includes when you're actually practicing.
Anyway, I've competed all of the questions once, done over 2,200 MCQs and have about 200 MCQs left until I hit review stage. I'm trending at 87%. I doubt I will get through the 200 before my exam Friday because I want to focus on all the problems as a whole, not just the few that I haven't gotten correct, but I feel like the mcqs and sims have me well prepared.
I would say go by the Ninja guideline of trending 85%. When you're in the adaptive stage and you get close to review stage, your trending will begin to go up but stay aware of your average score (not average trending), as well. Mine is 70%, I think. I would like for it to be higher but this includes all of the questions I have ever completed and I was getting 50 and 60% when I first began so I feel like that is bringing down my average. Overall, I feel pretty prepared for the exam.
In my opinion, you know you're ready when you can clearly think through most answer choices, explain to yourself why an answer is right and why the others are wrong. Nothing catches you off guard, and you know everything in depth enough to understand the questions and the details within it. With my first take of FAR, I was memorizing what the answers should be just from doing them so many times. My explanation for why an answer was correct was “because it just is.” I now have a better understanding of all FAR topics and can explain why answers are right and why others are wrong, and not just because they are!