Spyder Cube - anyone use it?

I was given a Sypder Cube for Christmas which is apparently a great little RAW colour calibration gizmo.

I've not fathomed out how to use it yet although it sounds promising. Has anyone used one of these and what is your feedback? Is it more useful in some circumstances than others, or is it just a it of a pointless gadget?

Any feedback would be fab!

Thanks