I agree with Ryan and Sixer that having and using two ground screws on devices would lead to 250.148 violations.
250.148 in part
The arrangement of grounding connections shall be such that the disconnection or the removal of a receptacle, luminaire (fixture), or other device fed from the box will not interfere with or interrupt the grounding continuity.
Frankly, I wish they only had one connection each for the hot & neutral also, making it impossible to depend on the device for circuit continuity.
I can not agree with that.
You are free to pigtail the device if you want but assuming proper installation it is not unsafe to feed through a device.
Bob
