They technically are meant for rimless, but you can get it to attach without modification. It was too much light for my Evolve 4 so it had been sitting around for a year doing nothing. If you REALLY needed to, you could just easily cut into the rim to make a slot, but I didn't. I suppose if it gets bumped the wrong way it could fall, so I may end up doing that.
I really wanted an AC20, as I use an AC50 on my 30gal. I haven't used this Aqueon yet so I may return it (I was going to replace the cartridge with a custom media setup).
I am very interested in ditching the carbon inserts I use in my filters (I have an Evolve 4 that I basically have the exact setup for an AC30 inside the media chamber) and using Purigen, but I do not know how to use it. I do not have any water clarity issues, but I hear it is still better regardless. Did you have to make your own bag for it?