Its definitely cardio-oriented but its a killer form of conditioning. It depends on what your goals are- if you are going for size then not sure the increased cardio is what you want. But the type of action is quick, fast, punch - i.e. explosive power vs slow, deliberate, endurance. I kind of think of it as a full body sprint.
I do know people who just cut the hell up doing it - girlfriend of mine was a natural BB and ex Army boxer - it was the boxing that cut her up for competition - mind you that natural FBBs have a helluva time getting lean enough w/ the estrogen issues and she would rip up like crazy.