Hi - new spa owner here. Is the following info (from the OP) still valid?
The best investment you can make in your pool is a top quality water test kit. Accurate water test results will save you time and money again and again. The TF Test Kits TF100, Taylor K-2006, and Leslie's Chlorine FAS-DPD Service Test Kit are the current stand-out choices on the market. All three include the FAS-DPD chlorine test, and are based on Taylor chemistry.
The OP was in 2008. Are there new (updated) kits that you recommend. Thanks!!