Its actually not a cleaner, its a dressing, a very good one LOL.
You will still need to blast out and clean your inner fenders first to get any dirty and grime out of there. But this dressing is a spray on walk away type of product, so you don't have to try and reach back in there, scrape and squeeze your hands, etc to get a nice blacked out looking wheel well.
It lasts for a long time as well and makes cleaning the wheel wells after that much easier.
Its a great final touch to your detail as so many times when you get done, the sun is low in the sky and hitting the side of your car and all you can see next to your shiny paint is ugly, dingy wheel wells.
Heres an excellent shot of it used on the HUGE gaps on a chevy tahoe:
