I have a GG DA with a carpet brush, green, so far it works pretty well. I use it with APC 1:15. It takes out a lot of the elbow grease, but you still need a tooth brush and another brush for tight corners and creases. It works well on leather seats, cloth seats, carpets, door cars, kick plates and such. I wouldn't use it on headliners. On carpets you need to use very little pressure otherwise the brush will boggle down.
After spraying APC(i use a gardener pressure sprayer) use the da brush on speed 3-6. I do 4-6 section passes then wipe dry with a terry cloth towel. The towel picks up a lot of dirt. The DA and brush just lifts the dirt so it can be lifted off. For carpets you really gotta work the cloth to pick up everything. Leather/vinyl wipes off easily.
Also for carpets I will spray alot more APC or combine with water. cloth seats and leather don't need as much apc. For removable carpets I take some dawn dish soap and water and really sud things up. I put it in an outdoor sink so suds aren't everywhere, then you can rinse with a hose and use a blower or put in the washing machine on spin cycle. Really dirty carpets I will put in the washing machine on gentle or normal cycle, on high end cars the backing will fall apart, but on cheap rugged plastic backing carpets it works just fine. Even soaking in the washing machine with white distilled vinegar or washing detergent helps speed things up.
Be sure to vacuum before spraying APC. Also be careful on some plastics APC will remove the colour, same with reconditioned leather.