In reply to George_Surf:
I went through this a little while ago, and went for WC Zeros. Each cam has a rather greater range, size for size, than the equivalent DMM Dragonfly, so your chances of picking the correct cam for the placement are better. Aliens have an even better range but they're not re-slingable.
There was some question, when I posted about this last, whether the differences on paper were down to the way that WC and DMM measure their expansion ranges. With both models in front of me and a set of calipers, they are both pretty damn accurate (interestingly, the figures both companies quote are from absolutely retracted at the small end, to about 5% retracted at the large end). It really does seem that the Zeros just have a bigger range than the Dragonflys.