ESSM customers include United States,Australia,Canada, Germany, Greece, Japan, Denmark, The Netherlands,and Norway. Countries in the process of integrating ESSM are New Zealand, Spain, Turkey, and the United Arab Emirates. The claim of success is based on extensive testing against MQM-8 Vandal, Boeing/Zvezda-Strela MA-31 and GQM-163A Coyote employed as non-recoverable target vehicle.
The Boeing/Zvezda-Strela is especially interesting since it is based on the the Russian AS-17 Krypton a member of the Yakhont/Brahmos family purchased from the Russians in the mid 90's.
I've said this before a supersonic anti-ship cruise missile is not a new concept, self respecting navies all over the world have had effective counter measures for at least a decade.