I use C2 from the r051, and I must say it went very further and improved along the way, from what I have tested, HTML5 is nice, I tried something on mobile, no problem it seems for now for the different project I have tested, I still think I'll encounter problems maybe when graphics will come (and even then, I know how to deal with that), but I know how to deal with that, the audio will be the pain
I'd love to see one day C2 having a native exporter, but HTML5 is good (for me at least)
As for optimisation, I didn't do a lot, but what I consider not a lot can be considered as "OMG how clean your code is" by others, C2 does need to be understood, and you still need to work hard, but in all honesty, I have never had any problem to organize myself, start by learning the engine, then begin to build a way of work, I might translate the article I am writting about this, it could help people going to the good way.
I have never feel cheated by C2, It does teach well programming by itself in my experience, however, I must admit that the lack of native support can be troublesome for some people.
Ludei and their cocoonjs thingy on the other hand.. I have never trusted it, I have much more facility into getting things to work inside chrome for android for now (and my phone is really not that great).
As for a CC based C2, the problem was the stability of CC.
I love C2, I love how it handle HTML5, I wouldn't even be the shadow of a bad programmer without it, now I am much more organised, I know how to deal with big project, I know also how a game works and should work behing the scenes, and the performances problems (not a lot I must say on PC) forced me to learn to program in a good way, which is truly great, and it seems on mobile that works.
I'll keep using it for now, and for a good time I think. And if not, well, I know the way video game programming works so that should be not as hard as it might have been.
My 2 cents (looks much more like a dollar but whatever)