In reply to Wile E. Coyote: I have a green one. They are surprisingly bomber. They do work best in parallel cracks and obviously are large so as Toby says have limited use in the UK. However they do have some distinct advantages over large cams:
They rack MUCH more neatly
Thay are lighter,
They don't walk
They are multidirectional
They are easy to remove
They are actually just as easy to place as cams once you get used to them.
Disadvantages are:
Not EC marked so unavailable here by and large
You can't leapfrog them up cracks to give you constant protection
They can feel wobbly if the sides of the crack aren't parallel