I have some Oopas and to me, they're just very different slings.  Different looks to them.  Both are comfy.  The Oopa is waaaaaay more lightweight and awesome for warm weather.  The Oopa is also easier to adjust than the CXD.  But by the same token, I find that I'm needing to readjust my Oopas, whereas I never have to readjust the CXD.  Also, my CXD has med steel rings, whereas Oopas all have large aluminum slingrings. This doesn't matter to me, but I know it's very important for some people.