From the NYT
In the game’s traditional mode, you need only use five white keys, which can be challenging enough. But switch to Pro Keys mode, and all 25 black and white keys begin to come into play. By the time you reach the Pro Expert level, you are playing what are meant to be note-for-note re-creations of the actual keyboard parts, if any, in the game’s 83 songs. (There are also around 2,000 more songs available for download.) The keyboard also includes a MIDI output for connection to computer music software like Apple’s Pro Tools.
But as impressive as the keyboard is, Rock Band 3 truly shines because of its new guitar. Sure, you can play Rock Band 3 with any older Rock Band peripheral (and most Guitar Hero devices), but this re-creation of the classic Fender Mustang costs $149.99. Coupled with the Rock Band 3 software, it could be the gateway to real guitar-playing for many people.
This device has six physical strings down where you strum, but the neck is covered with 102 thin horizontal buttons corresponding to 17 frets (multiplied by six strings) on a real guitar. And so with this guitar you unlock Rock Band 3’s Pro Guitar and Pro Bass modes.