None of the inexpensive testers (less that several hundred dollars) I have seen are very reliable. Most of the soil pH meters that sell for less that $100.00 have been found to give the same reading whether testing garden soil, Vinegar, or a baking soda solution. For a good, reliable soil test contact your local office of your North Carolina State University USDA Copperative Extension Service.

Here is a link that might be useful: NCSU CES

Last fall, I bought a kit called 'rapitest'. I got it right after I sent in some soil to my local agricultural extension office for NPKpH testing. The results were effectively the same.

I will probably do another extension office test this fall to check for other factors, but for estimates of NPK and pH, I'll continue to use my soil test kit.

Rapitest makes a soil test kit that does a very good job. It does require a bit of work, getting soil, mixing with water and then we the capsules. It is well worth the time it takes to get effective results.

Here is a link that might be useful: Soil Test Kit