I am the very proud owner of the Yamaha VKB-100 VOCALOID.
If you're thinking of buying one, it's not for you. The midi out is usb only and you need to turn the setting back on after every powercycle using an app you can only get from the Google Japanese store. The 13 (Thirteen!) built in instruments sound like they're taken from a PSR series and you can only have one effect in action at a time, from a list of reverb, trem, chorus and distortion.
However, I love it. It sings* in Japanese, which is why I wanted it.
*The singing is a bit jerky