I gave up on Polymer. I can't really explain it well but nothing worked as you expected it to. v2 was just hacked v1 (hybrid?) and so trying to actually figure out how to use v2 was impossible since every major custom element was hybrid. The documentation was bad, and the things you might want to use were somewhat depreciated, but you had to figure that out on your own. Then the standard glacial pace of development means that v3 was announced over half a year ago and as far as I can see, nothing has happened.