I have had an opportunity to utilize the Gyeon Fabric Cleaner a few times on carpeted surfaces. I have used it enough to view it as a solid product. Good for medium soiled fabric, without unusual issues.
It did not blow me away, but after use I found it to be a solid product. Although I have an expectation for severe issues or unique staining, multiple specialty interior cleaners will be a better alternative than any single fabric cleaner. If you make some effort to maintain your interior and do not make your car into a dining room or kitchen, it is a great product.
To apply, I sprayed the product liberally onto carpet.
I used the Gyeon leather brush to agitate the product. I then wiped the dirt and grime that was encapsulated with the cleaner away with the Rag Company RagnRoll microfiber towel.
Again, I would not suggest that this product really stood out. But I believe it to be a solid product on light to medium soiled areas. It works really well on the surrounding plastic parts as well.