The Pro29 Lefty takes the incredible design characteristics of the PRO29 SL and adds a Lefty Headtube, so you can run the lightest 29er fork available, and PressFit30 Bottom Bracket (which requires BB30 cranks).
Strengths: Fast, light, stiff but not harsh, great craftsmanship, very responsive, climbs like a mule. It turns heads.
Weaknesses: Absolutely none
This is absolutely the best bike I have ever ridden. I used to ride a lot of FS bikes but never again. I am sold on 29er hard tails! Climbing is effortless, the frame is laterally stiff, and very responsive. I can scream down the single tracks with confidence. Combine this bike with Stans wheels and tires and it's unstoppable, it just keeps on rolling over everything. I love the feeling of pressing on the pedal and accelerating without lag. I immediately felt I was a better technical faster rider.