You can go to Walmart, and get a cheap OTO/phenol red kit. OTO is not super accurate, but it is super reliable: if you get a ZERO reading with OTO, you have zero chlorine. If the chlorine is 10, 20, 40, or even 80 . . . you will still get a positive result with indication of the level, as the OTO gradually goes from yellow to orange and finally brown.

If you get a zero reading with DPD color matching . . . you might have zero FC and high CC or you might have high FC, or you might actually have zero chlorine.

The K2006 overcomes this problem, and allows accurate measurements up to around 40 - 50 ppm, and fairly accurate distinction of FC vs CC, where OTO only gives a crude and tricky distinction and tends to only give TC (FC + CC) results.

Also, it may not be clear from Chem_Geek's post, but YellowTrine (sodium bromide) turns your stabilized chlorine pool into an unstabilized bromine pool, which can lose ALL of its chlorine or bromine in a couple of hours.