I've developed a couple of WebGL games, and am trying them out on Android. I found that they run very slowly on my tablet, however. For example, a game with 10 sprites or so runs as 5fps. I tried Chrome and CocoonJS, but they are comparably slow. I also tried other games, and even games with only 5 or so moving sprites are this slow. This seems inconsistent with reports from others, such as this benchmark. Typically, when people talk about HTML5 game performance, they mention well-known and higher-end phones and tables. While my 7" tablet is cheap (I believe it's a relabeled Allwinner tablet, apparently with the Mali 400 GPU), I found it generally has a good gaming performance. All the games I tried run smoothly. I also developed an OpenGL ES 2 demo with 200 shaded 3D objects, and it ran at 50fps.
My suspicion is that many low-end and white-label devices may have unacceptable HTML5/WebGL support, which means there may be a large section of gamers you will not reach when you choose this as your platform. I've heard rumors about inconsistent performance of HTML5 and WebGL on different devices, but no clear picture emerges.
I would like to hear if any of you have had similar experiences with HTML5 or WebGL, or whether I can find information about the percentage of devices I can expect to have decent performance.