Unfortunately, logon via Twitter fails with 500 error bar flashing at the site's top and logon via FB fails with "App Not Setup: The developers of this app have not set up this app properly for Facebook Login.", so I can't try it.
Nonetheless, my biggest worry is why this is a service instead of a standalone package. (Actually, I've considered trying with the hope plugin may be possibly FOSS and if so researching whenever it could be hacked to be used with locally-installed Solr/Lucene server) I'm not really comfortable with directly or indirectly sharing my browsing history with most third parties.