AesopWatt :
As other said, the scirra arcade is bad, it was planned to be changed, but it did not for some reason I am not aware of.
Performances wise, C2 on desktop doesn't have too much issues, on mobile it is another story (but still doable), but all in all, C2 is notorious for bad performances because mainly, since it targets non programmers, people just assume that it should also target people that don't design correctly a game, on top of that you add complaints from people actually trying to make a game running on a weak phone while only testing on rather powerful PC (rule number one of multiplatform: you target multiple platforms, and not all platform is as powerful as others, so keep testing on a low-point target). There are also people trying to begin with one enormous project, that ends up learning to use the tool while doing it, which can ends up with a lot of little+big mistakes being made.
Also C2 is, contraty to belief, pretty open, and thus is easily prone to the user doing non-sense that is functionnal, but far far from optimal, C2 makes the programming easier, but you still have to design it carefully, without letting the game do too much useless things (although on PC it seems even really bad design seems to work well sometimes due to the actual performances of the engine + browser that are really good).
And to finish, the development time of a game in C2 is pretty good, but for more informations about how to design well a game, and use the tools C2 provides the best way you can (while keeping everything clear and organised), there is the manual, the experience will help of course too, and soemtimes tutorial, but I'll say be wary of tutorial, sometimes they are more functionnal than clean, so always try to get what is behind something that works in a tutorial so you can use it the best way you can think of (that is also applicable in other engines I guess, always try to see what is best when it is needed).