The people "against" roller matts and socks in general believe they trap and hold nutrients that are better exported. Even if you change regularly, those particles are still in the water column rotting and decaying until you change socks, or the matt rolls up out of the water.Its a roller mat, specifically the red sea 1200. They take the place of filter socks in your system. You definitely don't need one, but man are they nice lol. I used to run filter socks on my previous tank (180 gallon display) for years and would constantly swap them out in the beginning. Eventually I just took them out since I got tired of changing them and washing them.
There seems to be some pushback by some people against the roller mats on this forum, I'm not sure why. Worth every penny IMO.
I ran filter socks (past tense) on my store-bought sump, but I do not have on my DIY Sump. My water is every bit as crystal clear as anyone running socks/matt. I use a DIY flocculant version of a Coral Snow to keep my water clean, it also adds CA to my system (added bonus IMO, my CA stays about 440 using IO Reef mix for salt).
Run socks or a matt if you want, don't if you don't. At the end of the day, it is your tank, and you will do it how you want. Happy Reefing!