Ok let me give an example of how the TF-100 is better than the K-2006C
The FAS-DPD FC/CC test process uses R-0870 powder, R-0871 drops and for the CC portion also R-0003 drops
The standard TF-100 includes 1- 10 gram jar of R-0870 powder, a 60 ml bottle of R-0871 and a 22 ml bottle of R-0003 drops for the CC test.
The XL options doubles the amount of R-0870 and R-0871
The K-2006C includes 1- 10 gram jar of R-0870 powder, a 2 ounce (60 ml) bottle of R-0871 and a 2 ounce (60 ml) bottle of R-0003
Now at first you are going to notice that you have a bigger bottle of R-0003 with the K-2006C, and you will think this is a good thing, when in reality it is excessive, because anytime you do a FC/CC test you will only use 5 drops of R-0003, where you will use 2 drops of R-0871 for every ppm of FC or CC in your test sample, plus one drop each to confirm the color change has stopped.
So lets say you are running a typical pool with 40 ppm CYA, and an FC target of 5 ppm, and all is perfectly on target, your test will use one tiny scoop of R-0870 powder, 11 drops of R-0871 for the FC test for a reading of 5.0 ppm, 5 drops of R-0003, then an additional 1-2 drops of R-0871 for a total of about 12-13 drops R-0871 and 5 drops of R-0003 used. This is a best case scenario if you were running a higher CYA, your FC would also be higher and use more R-0871, if you were fighting algae and performing a SLAM procedure with a CYA level of 40 ppm your target FC target level would be 16 ppm, plus you would likely have some CC present, and you would be using 34+ drops of R-0871 and still only 5 drops of R-0003. So while the K-2006C may give you those nice neat matching size bottles, it is not something you necessarily want once you get into doing the testing.
Ike
p.s. I too recommend the Speed Stir, I don't think anyone has ever regretted spending the money on it, but I will say those that have done the test all by hand particularly all the hand swirling on the CH test, are the ones that are the most appreciative, so decide either buy it now and think oh thats nice, buy it later and think oh how did I ever live without this, or don't buy and and do things the hard way.