REASONS TO BUY
Narrow head gets in tricky placements other cams can't
Great holding power
REASONS TO AVOID
Expensive
Heavier than most other cams
Can get easily bent
They are ideal for Yosemite and Zion aid climbs, but a set is also nice for any area with weird pods. Which is just about everywhere except Indian Creek. On a typical wall like The Nose, Zodiac or Lurking gear, we recommend 2-3 sets of regular X4's and 1-2 sets of offset X4's.
Only downsides are they are a little heavy, expensive, and easily bent. But those are all part of them being just so skinny and sweet.
The Black Diamond Camalot X4 is a similar version, but are not offset - this cam wins our Editors' Choice Award, as do the Black Diamond Camalot, one of the most popular cams on the planet.