i run a closed loop with an OM and dart, and really like that it is pretty much hidden, but as pointed out, its a lot less energy efficient than PH's. four tunzes i think use about 50watts, as opposed to a dart at 100+. setting up, and plumbing a CL is not easy either.
one potential option for PH's if you dont want to see them is using those fake rocks that hold the tunzes, that along with some sneaky cord hiding could give you a nice setup.
also, my first CL setup was pretty loud, PH's are almost silent.