Generally, this option is intended for those homeowners who are having some problems (algae, especially) with their water clarity and will need to do quite a bit of testing. If your water is clear and you don't test a lot, you don't really need this.
It is also ideal for those folks doing a baquacil conversion because of the high chlorine levels you will need to test.
Its third purpose is simply to give you the choice of saving some money on the two refill items you will likely need first.
The R-0871 (2oz bottle) will not fit inside the K-2006 box, but can be used to refill your smaller bottle