Someone on amazon recommended "the fix" which i gather is a gimbal protector to prevent separation. Is this necessary in addition to the uavbits camera guard?
Do the new Phantom3's have this problem?
No, they don't. And the V3 P2V+ doesn't have the separation problem either. DJI redesigned the rear motor housing assembly to prevent this problem. Go through the forum and see how many motor separation incidents have been reported on the P2V+ V3, you won't find any. Don't believe everything you hear/read, a lot of it is BS and old information.
I have the camera guard from UAV BITS:
I originally bought it because I was looking for something to protect the camera from below in the case of a crash. Since I've never crashed, I cannot confirm how effective it would be in that case.
To install it, you just need to place it between the landing gear and attach 4 zip ties. It should only take a few minutes. There are no cons as far as I can tell. It does not negatively impact the flight in any way.
I have found that it prevents grass from interfering wth the camera when taking off from grassy areas. If you have a GPS tracker, it's also a good place to mount it. So, there are some benefits outside of its intended purpose.