Just select kits that include reference standards, eg, Seachem Nitrogen
Check the fine print (or contact technical support) as to whether kits you have are suitable for freshwater use, some are, some aren’t
Hobby test kits are a breeze to use, and can be reasonably precise and “accurate enough”
But
they are only as good as the operator
Check your water supplier for tap parameters - most have some online data (and more detailed information available upon request) - as that will give you a known starting point
I fail to see why the range of possible freshwater values would generate inaccurate results ... any time you measure an endpoint parameter for a kit, standard procedure is to then dilute the sample with RO water and test the dilutions
I rarely test my tanks (anymore) - fish behaviour/activity is generally sufficient (but also depends on a level of experience), I do keep some 5in1 etc test strips at hand so I can check tap vs tank parameters