I bought the unit from a shop in Canberra (Australia) called Pro Audio. I paid $AUD1030 for the unit. I wanted a rack mountable unit that could be controlled with a Midi foot-controller. It has all your standards such as Reverb Chorus Delay Phaser and flanger. However the real fun is in the newbies like Envelope Space Warp and stuff like that. Also you can string series of effects together to create your own sounds.
The user manual is awesome! Also there is a Factory bank of 100 presets along with a user bank of another 100.
The main criticism I have of the unit is that there is a slight delay when changing between effects. This makes it hard to swap effects whilst playing live. However if you get a volume control pedal (like Ernie Ball's pedal) you can program the unit to turn off the effect when you rock the pedal in a particular direction.
The Quad 4 is a robust rack mountable unit. It has an easy-to-use digital interface. The user manual is excellent and in no time at all you can get started. The quality of the effects is outstanding.
The Bottom Line - a sturdy easy to use effects processor with 100 user presets. The effects are awesome in quality. If you've got the money I would recommend this unit (and a foot-controller) as an alternative to traditional floor effects processors.