I recently built one of these from the RxR kit. It is all stock and I use a 1000 mAh 3 cell which gives 8-9 minute flights. Overall it flies very well - I was impressed at how nicely it flies. I did have a couple of problems with the kit though.
First off I flew it on grass before the water and on one landing I hit a thick spot in the grass and it decelerated fast, and the wing came off! Turns out the wing mount was just stuck on with some lousy glue that didn't stick. I'm just glad it didn't happen in the air.
With the wing off and the mount attached, I could see how much it was deflecting the aileron pushrods. I've attached a picture of it and you can see that it is just about ready to snap off the servo arm. I put the connectors on the bottom of the servo like suggested in post #1036 and it was much better. After that experience, I trimmed the wing tips too as suggested in the post.
I just flew it off the water a couple of days ago and it is even easier than flying it off the grass. It runs on the water so smooth. I've attached a video with clips of two flights I got on it. You can see from the water surface that the wind was variable and it was a bit bumpy at times, but the plane handled it well. On one landing I even touched with the wingtip first with no tendency to water loop.
This is my first sea plane and I really enjoy flying it!