It makes your brake alot stiffer. Instead of the pad hitting the rim and the pad backing flexing it pushes the pad into the rim with minimal flex at all giving you a better brake. It also makes a slight difference on the feel of the brake on the lever. One tip though - Make sure your pad is hitting the rim exactly square becuase as there is no flex in the backing your pads will wear at a angle very easily.. If you are on about the Red CNC pads that are from Poland or somewhere then they have had some good reviews. You can pick soft or hard compound when ordering - Soft for smooth rims and the hard compound for ground rims.
I'm currently running both grinds front and rear with Heatsinks on the back and Koxx Reds on the front. I ground the rim originally with a harsh grind and put a new set of Heatsink Yellows on. The brake was seriously crazy. It locked up instantly, giving you absolutely NO modulation. I found this hard to control the bike at times, with the power ever beng ON or OFF. I sanded the rim down and put these pads on and it is much better. Light grind and a decent set of pads is wicked! If your looking for a cheap decent set of pads then i can Recommend the Onza Lime ( green ) or citrus ( yellow ). Although, i would also recommend a seriously LIGHT grind as these pads wear down very quickly.
Hope some of this will help you!
Sam