It's funny how much misinformation people can give. It DOES increase flow through the media. Water goes in the top, with four sides giving the water nowhere else it can go, where do you think it will go then? That's right, down through the media and out the bottom. It's not rocket science. It helps to trap more detritus because it forces the water to flow over the floss. It helps water quality because it forces water to flow through the media. Then you have convenience, it gives you a place to put all your media without floating it in your tank. Very easy to install, very easy to maintain and change media, and filters. If you keep the stock setup, those filters clog fast and you need to replace about twice a week. They're not cheap. So it would pay for itself in no time by not having to buy biocube filters. Even if you don't want to buy one, you could build one like I did. It's a good thing to add. Like a sump on a bigger tank, not necessary, but makes it much better. Here's the one I built.
hope all this helps. Another advantage is that it also frees up half the second chamber. I put a fuge basket with chaeto in there, or it gives you room to run a skimmer. To me, that's a HUGE advantage. I have 0 nitrates, and undetectable phosphates.
Mike Hayes