HI - I recently got the K2006 Taylor test kit online. I purchased it specfically because it uses titrations to test which I understand are more accurate than the OTO method. It eliminates the "color matching" thing which I always found subjective. One other difference is that it can test FC, CC, and TC from .5 up to I think 50 ppm, as opposed to the K2005 which only tests Chlorine from .5-5 ppm. This is key if you are operating your pool at higher chlorine levels based on your CYA. It would also come in handy when and if you ever have to shock the pool.

Those are some of the basic differences, I think. Good luck.