Complexes are downright brutal. I use them with barbells, dumbbells, sandbags and kettlebells.
You can use them with stones as well. The bottom line is don't be afraid to go heavy with complexes either.
They put on muscle AND improve conditioning, but, most people fear them because they are NASTY once you get going with them. Your muscles feel like they're going to explode and your grip gets a helluva workout from the constant movement of the barbell in your hands.
Check out this video of some Dumbbell Complexes adding The Grip 4orce to make it even more challenging.
Here's a tip if you're busy as hell like I am.
C) D Ball Cleans x 10