Also, most inexpensive test kits are OTO and that is what 'newbies' usually have at their disposal
FWIW, if you are going to spend the money on a DPD test kit like the K-2005 you might as well spend a bit more and get an FAS-DPD kit such as the K-2006.
I have never come across anyone who said you cannot do dilutions with DPD and, in fact, have pointed out myself many times that dilution marks for 2:1 AND 4:1 are molded into the comparator that comes in the K-2005 and that the instructions for doing the dilutions are on the inside of the lid.