A show stopper for me is the unusable printouts provided by this browser and Opera. The font sizes are huge. This has been a problem for quite a while with Opera. I'm really surprised that such a fundamental bug doesn't get sorted as a matter of priority. Vivaldi seems to be a nice browser but I'm afraid I won't be using it because of this printing issue.
True, setting the magnification factor manually instead of relying on the "zoom to width" will be a required feature.
But apart from that, I find the print feature amazing, the overlay dialog works well and the engine can even print a website including IFrames (which are left out by MSIE and Mozilla).
It has even an integrated PDF exporter. Can't wait to see the final release!