No matter how approved it is, if the grounding connection
can be moved or compromised by normal mechanical vibration
(even kids running down the hall cause such vibrations), then
the ground is not sufficient. Approved ground make it
virtually impossible for the ground to be compromised by
vibration or receptacle movement when the power cord is
attached.

Not only do you want 'their' approval. The receptacle must
meet 'your' approval. Safety ground must remain fully
connected at all times - which is why the #10 screw that hold
receptacle to box, alone, is not sufficient as a safety
ground.

blueman wrote:
When used with metal boxes, do the self-grounding outlets provide as
good a quality result as using a separate screwed-in grounding wire?