The MP-GT1 can slow down (and speed up) any song without changing its pitch, making it much easier to master very difficult fills or solos, allowing you to learn at a speed you are comfortable with. It can also adjust the pitch to whatever key you want, which can be very useful to match the key in which you are most comfortable singing, or prefer playing. Once you have mastered your technique on a song, the Tascam allows you to perfect your own style by canceling out any recorded guitar that may distract you from your own playing. A built in tuner and metronome keep you sounding your best, while keeping in time.
This is a very useful gadget that will benefit guitarists everywhere.