Personally, I do not like them. Why?? The water is actually pretty heavy. Unless you have a very strong water return, you will have to operate these little gadgets with power heads. Regular power head might not be strong enough to make them work properly which in this case, do not serve their purposes. If the power head is too strong, then I would worry about heat generation or the smaller fish been stocked by the intake.
This is what I do. I am using two powerful external pumps and point them to each other to create swirls or whirlpools where the water is constantly hitting against each other from both side. In this case, no spots are missing and the current continuously spurring outwards. This is what I do right now. What kind of pump?? Check here:
http://www.reeffanatic.com/cgi-bin/category.cgi?category=pump_ep&item=PUMP_APG&type=store