I have tried a 6 week rotation of circuits. I found it fun, and liked doing them, but I find I get better muscle build from more concentrated gym-style work-outs. I cannot speak to the cardio benefits, because my cardiovascular system is extremely strong from swimming. So I cannot tell if that improved.
Why don't you try it for 4 weeks and see. It does not hurt to experiment with your work-outs and try different things.