I've been testing the Opera DEV 39 release for several weeks now because I'm particularly interested in understanding the integrated VPN functionality to be provided. I'm not an Opera 'power' user by any means - I've primarily been using Firefox on Windows. I've got to observations and feedback for the forum community.
Font display quality is poor (Windows 8.1). Compared to Firefox, Opera's text presentation is FUZZY at ALL comparable default zoom levels - verified in a side-by-side 'taste test'. I am current on my Windows fixes and have searched throughout the Opera forums to no avail to see if there is a problem with my configuration/environment. Most recent comments on this topic are very old (Opera 12).
Bookmark sync support is poor. No Xmarks support for Opera. It appears one can only do a 'one-off' migration into Opera which is useless for evaluation purposes. My bookmark library is fluid and the limitations of the 'import/export' paradigm is unproductive. I realize Opera can't force Xmarks to support its browser - but if Opera wants to make it EASY for people to start to use its browser in place of Firefox/Chrome/IE/Edge/Safari, there has got to be a better solution than the archaic import/export approach documented at http://help.opera.com/Windows/12.10/en/importexport.html.
I am hard-pressed to believe that these limitations due to the pre-release status of Opera DEV 39. If I am wrong, please correct my perception.