This is an academic paper that explored the real world use of fentanyl test strips (FTS). The study found that using FTS and receiving a positive test result was associated with changes in drug use behavior and perceptions of overdose safety.
Peiper, N.C., Clarke, S.D., Vincent, L.B., Ciccarone, D., Kral, A.H., Zibbell, J.E. (2019). Fentanyl test strips as an opioid overdose prevention strategy: Findings from a syringe services program in the Southeastern United States. International Journal of Drug Policy, 63, 122‐128.