Remote control:
FC40 has 5.8GHZ (like Phantom 2 Vision) up to 500 meters. This means that if you want wifi with a 2.4GHZ GoPro, no interference. Some speculate this may have caused many loss of control issues, however flyaways are still reported, uncertain of why, either user error, user initial procedure (startup) error, compass calibration, NAZA crashing, or other. No one knows.
FC40 from what I have read is Phantom 1.1.1, NAZA v2, dual antenna and one user reported that he tested with success in the assistant software the usage of the gimbal lever.
What are you losing? Well the included camera until you get another one, but the one included will still be good for other things. What else? I guess the certainty that the package including batteries are fairly new, I am only guessing.
If you are not looking a the Phantom 2 (either model), than the FC40 is a better buy than the P1, unless you buy it bundled in a package with cameras and mounts.