Yamaha Vocaloid by fiddler2007
ENGLISH version 4.3.0: Loaded as VST it causes a playback start delay of around 1 second in Cubase 8.5 and 9. The user interface within the plugin is OK and free of crashes etc, but there's a lot of Japanese not translated into English in version 4.3.0, especially the "Job" macro handling. Tried and tested it extensively with the "Ruby" Vocaloid especially suited as advertised early 2016.
IMO !!: you can use it for background vocals only, and you need to know your way around with tricks like pitch-bends, selecting decay % and vibrato type on individual words, extensive phonetic editing, and adding some extra symbols like a * to avoid occasional plops etc, not found in the manual.
It seems very stable though and found this quite impressive work done by an expert with stand alone Vocaloid 3: https://www.youtube.com/watch?v=R2EcFqLwNQQ