It won't actually mix though - for that you'd need 2 decks and an external mixer.
It is the functional equivalent of a DJ turntable - allows you to scratch, adjust speed, positioning, start/stop with differing abruptness etc. , just that you don't have to carry all those big round plastic bits with you...

IIRC, there was some talk of a possibly more consumer-targeted version where a single unit would decode/control 2 mp3s and mix them.

/Michael