Godot is not free, neither is Blender.
https://www.patreon.com/godotengine
You could also use Torgque 3D
http://www.garagegames.com/products/torque-3d/licensing
or Blender Engine
...
or Unity or Unreal Engine or ...
why is it not free? Someone has to develope the engine for you. And if nobody would pay the Godot-guys, who would do it? So OpenSource, fine. But who will read throu all the source and extend the engine? If you will, you pay it with your time as well.
AGK has no license fee. (Unreal Engine does 5%). So how much will your game cost? Assets, additional programming, marketing, Art, Music, Animation, Visuals, etc? You can see the source code from AppGameKit, I think, in tier2, so no benefits here.
Godot, AppGameKit, GameMaker, Unreal and so on, they don't make your dream game. You have to do it youself.
And, what does GIMP cost? To much time, so I am using Photoshop or Affinity Photo. Godot or Spine? Godot or Spriter for animation? And so on. To save some bugs on Godot, you would pay on other place in your tool chain.
Would be nice, to see a little project done in AppGameKit and Godot and compare the steps needed. On Paper Adobe Flash / Animate is great. But without realy using an engine, you can't tell for sure.
I tried Godot half a year ago and two years ago. In this state I rather would use Unity, but it's not programming, it's configuring the engine, till it looks like something gamish thing. AppGameKit works without youtube and without community help, without internet.
There is a great community, but also a great help inside. And I love the APK export