I am currently experimenting with Polymer 2 to create custom elements, particularly using the vaadin-grid at the moment. After compiling it to ES5 and loading that version in IE 11, I’ve found that the browser to hangs the moment I tab into the grid. I have not been able to reproduce this problem with MS Edge 14 (using my ES5 build), or Chrome 58 and Firefox 51 (using my ES6 build).
Personally I detest IE but the organisation I work for stubbornly refuses to move away from it, unfortunately, so I won’t be able to progress using web components if they don’t work in IE 
I only went with version 3 of the grid because I couldn’t get version 2 to work. Anyway, just letting you know that keyboard navigation using the tab key isn’t working (for me, at least) in the latest beta.
Thanks.