A tds meter is completely unnecessary in soil. Been growing in soil for years without one. Its used to monitor ppm of water, mainly used in hydroponics to know when the nutrient amounts drop or rise in the reservoir and when to add more nutrients or more water to balance it. In soil you cant exactly test the amount of nutrients still in the soil, at least not any simple way i know, so you really dont have any reason to use a tds meter. Just learn signs of deficiency and toxicity and adjust over time based on that
Also ec meters are better because tds meters dont really read ppm, they read ec and do a conversion to estimate ppm. Some go by a different conversion because ppm and ec dont directly relate, so while one meter gets a reading of 1,200 in your water, another may have a reading of 1,500, with the same ppm. Ec is always read the same