I use complexes for warm ups and for conditioning. I found that even though I'm huffing and puffing, the affect is not quite the same as other more "aerobic" activities. As far as "replacing" cardio, I don't think it would replace cardio completely.
I use circuits of BW exercises, DL's, squats, cleans, snatches, calisthenics, rope jumping, and treadmill incline runs/walks for my cardio. I set up 3-6 exercises and do cycles of 30 sec of work and 10 sec rests. As I progress I will increase my times to like 45 sec work and 20 sec rest - then work my way down on the rest periods . I found that the little rest between exercises allows me to last longer than what I might if doing complexes. I guess a comparison could be the circuits to jogging/walking and the complexes to HIT.
Just my opinion.