I assembled an LT40 ARF and found the surfaces warped as they came out of the box. I used a heat gun and blocked the surfaces a little past straight in the opposite direction. I was never really satisfied with them. If I had it to do again I would build then new from scratch with straight material.
I ama builder from a long time back and this was only the second ARF I've ever tried. I don't know about the kit built version but my ARF was very tail heavy. After compensating for that problem it flew fairly well with a .46 engine.