Soil pH is useful, but a cheaper alternative to a meter would be a soil pH test kit. Cost about $15 (£12). Every few years, or more often if you want, send a soil sample to a lab for a more thorough soil test, pH and nutrient analysis.
pH meters that are offered for £20 or so are nearly useless because they can't be properly calibrated (a proper pH meter will be £200 to £300 and up, plus necessary supplies such as buffering solutions).
Why is pH important? It has to do with nutrient availability to plants at different soil pH. See
https://www.canr.msu.edu/news/more_reasons_for_soil_testing for a useful chart, note that most nutrients are most available when the pH is around 6.5 to 7. Note that nutrients are available over broad ranges of pH. You just need to know roughly where you are in terms of pH to determine if your plants will be able to get necessary nutrients. For example, using the chart, if your soil pH is lower than 6, your plant will struggle getting enough phosphorous. Soil pH is easily raised by liming the soil. Brassicas require boron, but will struggle with boron availability if pH is near either 4 or 8.5.
Another useful link explains what specific nutrients do for the plant, and how to recognize some nutrient deficiencies:
https://nrcca.cals.cornell.edu/soilFertilityCA/CA1/CA1_print.html This article focuses on plant micronutrients:
https://www.cropnutrition.com/nutrient-management/micronutrientsDo you need to worry about testing for all of the micro and macro nutrients each year? Probably not. Provide the main macro-nutrients each year in the fertilizer of your choice (manure, blood meal, etc., or a chemical fertilizer if you prefer). Adjust soil pH as needed. Provide calcium, magnesium, sulfur (gypsum and Epsom salts as needed). Most of the remaining micro-nutrients will only rarely need to be provided.