I purchased the P2 with gimbal. However, I thought I would learn to fly it before attaching the gimbal. I do not know for sure, but the P2 when sold with the gimbal may be calibrated so that if the gimbal is not attached it will fly slightly out of whack. This will panic a newbie (like me). In my case, the P2 wanted to drift away from me and I had to pull back the stick just to stay in one place (yes, GPS mode was enabled and working).
I decided to go ahead and learn the software, firmware upgrade, and calibration. The software detected that I did need to calibrate for level (this is why I assume it was slightly off without the gimbal). I calibrated (still with gimbal off), upgraded the firmware, calibrated, and bam! Perfect flying.
My advice before the first flight is:
(1) If you bought the P2 with gimbal go ahead and install the gimbal.
(2) Check for firmware updates and calibrate.
(3) They warm you not to use Naza but I think that is crazy advice. Activate Naza so you can activate IOC. I would not set S1 to allow for manual flying at this point but definitely activate S2 modes (IOC). HomeLock is a must for first timers. It is the panic button.
(4) Also set max ranges. I set to 400 ft altitude and 800 ft range (my estimate of the size field in which I was flying) until I was comfortable.
Hope this helps. I am open to others disagreeing that the P2 with gimbal is calibrated for them together and will not fly right without the gimbal but this was my experience.