I believe a bright 4th grader could test water accurately using either the K-2006 or the TF100. As stated above, same tests, same reagents, same instructions.
Can you count? Can you multiply? Can you tell red from purple from blue from green? You can do this.
The worst test for colors is pH, as it is more shades than actual color changing. And if one holds it at arm's length with a white background, it's not all that difficult to see the differences and decide is it 7.5, or is it pinker, and if so, is it closer to 7.5 or 7.8?
The payoff for a good test kit is sparkling balanced water. The ability to toss a coin in the pool and tell from the deck whether it's heads or tails. Or stepping out on a calm morning when the water is totally still and having the pool look empty. It can cause a bit of a shock at first glance, I'll tell you from experience! Last year my wife's best friend brought her daughters over to swim. They have a pool at their apartment. One of the girls said she likes swimming in our pool better because it's clearer - innocent honesty!