I do play back. And my Karni can on a full tank of mine do 2500 shots. I use a 92/4500 HPA tank. The reason I am getting the DM4 is to have a back up marker. And my karni to be honset was down most of the time this season (the pump arm snaped and it took 2 months to get it replaced). So, if i like the DM4 I will sell my Karnivor 2 and get me a DM5 hehe.
And no weight is not a problem.
EDIT: Still waiting on a nice trauma DM4 picture