My comment that it was a gimmick meant that your tank will operate without it. It's nothing but a "hey im shiny and I move, buy me" type thing. Yes, it holds some of the nitrifying bacteria, just like ceramic media, just like the walls of your tank, just like your substrate, just like any decorations in your tank, and just like any other submerged surface. It's unnecessary, and imo can subject your tank to mini-cycles when it stops moving as observed by others in this thread.
My reason for recommending the AC over the Marineland is due to media flexibility and the option to adjust the filter flowrate. I've owned both, and I don't care for the fact that with a Marineland biowheel filter I'm stuck using their media inserts which force me into using carbon. I currently use the Aquaclear, and while it is slightly noisier in operation (than a penguin without a biowheel running), I like the media flexibility that I have with it.