With so many arguments as to which testing method is best in the market, statistics have become more subjective rather than objective. Depending on the brand and price of water testing kits used, some may think that their test kits are cost effective than other methods.
Test strips are just as good as liquid testing and water analysis in pet stores. Any variance is generally within the acceptable margin of error. Unless they are subject to laboratory testing, the variance in the test results would probably be trivial to even cause you to overthink. Other aquarists get misled by inaccurate results of using test strips; however, this could only be caused by misuse or improper handling and storage since these are very sensitive to moisture and should be stored properly.