I just put a Rekluse Core Exp 2.0 on my 2013 YZ. Holy sh*& these things are way better than advertised. I have been riding tight single track for over a year and I cant believe I was even able to ride without this thing! It immediately made my life easier and built confidence. I was immediately able to climb hills better and climb up things I couldn't have before.
I was very skeptical on if the Rekluse worked all that well, but all I can say is wow!!!
For all the people that keep asking how to make their YZ better in the woods that answer is simple: Rekluse, 12 tooth front sprocket and 50-52 rear depending on how you feel. Then of course guards and you are good to go.