This is an incredibly unique pedal that can be used with a variety of instruments to give a harsh, electronic flare to any style of playing. I have used the pedal with my electric guitar, electric bass, drum machine and sequenced analog synthesiser all with excellent results. I have not yet used the pedal with my electric keyboard, but from my usage to date I am sure it will work well in this instance too. It works well in a chain of pedals (as long as it is placed in the start of the chain) and I find it goes particularly well with some subtle delay.
Pros:
Excellent design and quality.
Intuitive and easy to use.
Wide range of sounds and options.
Works across multiple instruments.
Using the square wave only works as a great fuzz pedal.
Cons:
Not exactly needed in all styles of music.
The tracking of very low notes on the bass guitar especially can be a little off, but this is only sometimes and not that noticeable.
Overall I would recommend this pedal to those who want to turn their instruments into chugging, synth-driven, corrupted madness (or those who just want a pedal that offers something unique).