The transition double may be more comparable but it aint got much rear travel only 3in. This would be better for street and park than the bottlerocket. I think you need to decide what it is going to be used for most then decide.
I own a Cowan DS and I am selling it to buy a BottleRocket. I decided that I want a little more suspension I don't ride street much, but I do dirt jump quite a bit. So I hope that the rocket can do that. Cowan DS feels like a bmx bike with some give. Also its aweosme concentric BB makes it super easy to Single speed.