1) Canvas+ is for Android
WebView+ is for iOS
Canvas+ is good (faster than Crosswalk)
and WebView+ is very smooth (I didn't check but @Silverforce did )
2) Recently I didn't experience audio problems on Android app
3) C2 loader is not visible in CocoonJS, but there was some post with information how can you fix it (so players will see loading bar or percentage); we could ask Ashley to fix it, but we all know the answer
4) You should remember that loading images on mobiles is slower than on PC. So it is important to optimize size of images (i.e. remove not neccessary images, change resolution) = you can save a few seconds of loading time.
5) The biggest issue is that now you can use only MoPub for ads. And MoPub means low fillrate and NO backfill from AdSense. So you will get #$#$$@# fillrate and $#@#@# eCPM.
there are Atomic Plugins made by Ludei, but you can't use them yet in @Ludei cloud service. Ludei told that they are still working on updating their cloud service.
When they will do that (= native AdMob in Canvas+ / WebView+) then CocoonJS will shine like a star
Usable links: https://github.com/ludei/Construct-2-plugin https://github.com/ludei/atomic-plugins-c2
Summing up: you can release your game without bigger problems (I think so) but we are still waiting for native ads...