BCI's get longer overall that Dum's, but the Dum's are more heavy-bodied and muscular. IMO given the same length BCI and Dum, the Dum is a much stronger snake.

That said my Dum's are also less active when being held than my BCI's, they're much more inclined to take a wrap or three around your arm/wrist/hand and stay put if you want to walk around with them.