What Mike said.
Litchi can't do IMU cals and some other deeper settings like rates. However, once you have done those with GO you don't need to use it for flying. I have never flown (as in left the ground) with GO (yea, I did spin the props a few times but GO crashed before I could push up on the throttle). I have only ever gone airborne with Litchi. And I am not sorry one bit that I bought it. I don't buy many apps and very few of them have I received my full measure of value from. Litchi is in the top of the list right beside Strelok and FoxFi as best value for your buck spent.
For me, GO would freeze or crash within about 2 to 5 minutes of trying to use it on my Galaxy 5s. Litchi, however, ran flawlessly. So I never trusted GO with >$1k of bird in the air. I did manage to get GO to run long enough to do IMU cals on my two P3s. Strangely, it runs fine on my nVidia Shield. But, because I lost faith in it out of the box, I still don't trust it. That and its full of NFZ and Geofencing restrictions Litchi doesn't have.