Thanks a lot for your opinion Chroma72. I'm into Unity myself, and like you say, Unity is a complex beast, even with all nice Plugins. The documentation is often a culprit and support sometimes good, sometimes nearly non-existent.
That drove me to the wish to have some 'lighter' game development app, but without being a dead end like - imho- C2 was, without putting all the complexity into, needed for exporting to iOS or Android or making a decent GUI. If I'm ok with complexity I can (and will) stick to Unity for being a fine 3D Software. But for small ideas, 2D and ok with HTML5, I need something easy on my mind, and with a much smaller package size :)
About the iPad Pro, another thing that annoys me about Scirra, how can they promote C3 being mobile development ready and even have a nice Video about it, when it's actually not. Trust is not build that way. Sincerity is not their strength unfortunately. That makes the decision not that easy, you know, cheat me once and so on...
So I think I will give the free Version an amount of my time and see how it goes. Then I will decide if the upgrade is worth it to me.