Here is a summary of what I've learned through first hand experience with OBD II readers/scanners or reported by others here on the Metris site.
These models do NOT work on the Metris:
Inova 3150f- I had one in my hands and tested it in Nov 2017
Launch CRP129 OBD2 Scanner Diagnostic Tool- I had one in my hands and tested it in July 2017
iCarsoft Genuine Mercedes Benz I980 Professional Diagnostic Scanner Tool- response to my question on Amazon by an iCarsoft representative
iCarsoft MBII for Mercedes Benz/Sprinter/Smart Professional Diagnostic Tool Scanner- reported by 2017MetrisCamper
FOXWELL NT301 Car Obd2 Code Scanner- reported by Tree95
Bosch ODB 1200- reported by Waterjerome
KW902 ODB II Diagnostic Code Scanner Read Phone Android ELM327 Bluetooth Torque (from EBay) cleared P4055 errors for the "Evaporative Emission Control System" (EVAP). I used this unit to clear the code and CEL- reported by etdown
Autel- I sent an email to Autel, which sells a variety of automotive electronic diagnostic devices ranging from the low end to high end ones aimed at auto shops, if they had any OBD II readers/scanners that worked with the Metris. Here is the response: "Benz W447 software is under development, we plan to release new software to our Maxisys scanners to support W447 in February. "
So Autel appears to be the best hope in the near future for an OBD II reader for the Metris.