First post, newbe here, 14 flights on a Phantom 3 A.  It is a Wonderful Bird, great success, so far, no problems.  Also have found this forum to be extremely helpful.  

I have two questions, one is has anyone tried the The Killer RC - Gimbal Saver?  The second is in the event of a crash, in which the camera Gimbal is destroyed, could I replace it with a 4K Phantom professional camera (on my 3A)? TIA..

As to the gimbal saver; personally, no.  

As to the 4k camera on a P3A it would appear so.  The specs sheet lists both versions http://store.dji.com/product/phantom-3-professional-4k-camera

And others have said replacing it with the Pro gimbal/camera is a go.

If you ever have to or want to rep[lace camera with 4k you must update  to Professional FW.

I have Killer RC gimbal saver on both my P3Ps…..though, in a bad crash there are many things that can break but it will prevent the dreaded separation.

Aloha,

     After witnessing the disasters with the P2 Vision + gimbal separation, I fabricated a gimbal saver out of a standard thin paper clip for my friend's P2 V+.  It worked like a champ!  Only recently did I learn about aftermarket gimbal savers.  When I got my P3, the first thing I did was make a new gimbal saver out of a paper clip again.  This saves a lot of weight and maintains the camera balance with no overkill safety.  I was really stoked to see the DJI P3 camera clamp fit right around it (forgot about that)!  Still, I have to check the gimbal status on the flight page to make sure there has been no distortion of the clip (so far no problems after dozens of flights).  A bit of Scotch Tape also helps hold things in place as a backup and is also lightweight.  But, this is not for everybody since you have to have a good eye and be able to use a needle nose pliers real well.  The best thing is to fly safe and do not crash though.

Aloha and Drone On!