We are using Konva for simple education games and the game editor at https://learnplayground.com and are mostly happy with it. It is easy to work with, the documentation is good, and so far supports all our use cases. The only drawback is some performance issues with animations on some browsers which we are not sure if we can fix by optimizing our code.
We have been using Konva for 2 years and would probably have chosen it again if we where going to start developing today
Yes, we target mobile browser and it works good in most. We did get a report that it is slow on Samsung browser for one user, but haven't looked more into it yet. It is also very slow on Firefox on Android, but according to some bug reports we found on Firefox it is because they have problems with performance on Android when using several layers of canvas. So as long as you don't care to much about the 0.5% who use Firefox on Android or don't need to use layers you should be good.
edit: you can go on https://learnplayground.com/games and try out free games if you want to test, but know that we are working on optimizing the game engine to work better on mobile so performance and scaling is not as good as it should be
We have been using Konva for 2 years and would probably have chosen it again if we where going to start developing today