Rock Band 3's newest features, you've secretly invested in a pair of fully functional MIDI instruments as well. Create Digital Music, a site dedicated to -- well, you can figure it out -- recently reviewed the two devices' capacity for real-life rocking; and surprisingly, they're both very capable in that regard.
The Mustang guitar may not have the authenticity of real strings, but at $150, it's one of the most affordable MIDI guitars on the planet. With Synth and Strum input modes, it could have some interesting applications for those creative types. The keyboard also received high marks for its ergonomic form factor and velocity-sensitive keys. In short, it's not the best keyboard on the planet, but it can (and should) be used as an actual keytar. Why haven't you bought this yet? You're wasting everyone's time.