The reason we recommend the "C" over the K2006 is because, in general, when people come to this site for the first time, it's because they have a problem with their water. It is either really cloudy, or green, and if that's the case, you will go through a lot of reagents to do the SLAM process. If you only order the 2006 without the "C", you will end up needing more reagents almost right away. The "C" is the more appropriate one to buy and also a better value in that you're getting bottles with almost 3 times the amount of reagents for a little more money.