Review comparing Acclima to another probe: https://acsess.onlinelibrary.wiley.com/doi/10.1002/vzj2.20013
Upshot: when soil is non-uniform, need to do careful calibration. Optimistic view: if you place some targeted sensors in particular locations, and develop some experience, you might be able to establish a local intuition around what the sensors are telling you ...
Great collection from Acclima regarding soil moisture sensors: https://acclima.com/research-news-acclima-soil-moisture-sensor/
https://www.mdpi.com/1424-8220/18/11/3786
Overview of various soil moisture sensor technologies: https://journals.ashs.org/horttech/view/journals/horttech/21/3/article-p293.xml
UMN overview of soil moisture sensors: https://extension.umn.edu/irrigation/soil-moisture-sensors-irrigation-scheduling
Review of soil moisture sensors http://ogallalawater.org/wp-content/uploads/2020/02/SoilMoistureMonitoring.Ogallala-Water-Resource-Guide-FINAL.pdf
Review of soil moisture sensing technologies and calibration procedures -- NASA -- https://lpvs.gsfc.nasa.gov/PDF/CEOS_SM_LPV_Protocol_V1_20201027_final.pdf
https://www.ars.usda.gov/people-locations/person?person-id=24443
Workshop on soil moisture sensors: https://twri.tamu.edu/media/1681/schwartz-imisworkshop3opt.pdf