Sufficient protection from what? The fact that you say"NO mouth/ nose..." sounds like you expect respiratory protection from it. The answer is NO.
The provide protection from one thing: straight line droplet projection, to your eyes, nose, mouth, facial skin. Nothing else.
We have a team of people in our church family who are tasked with trying to figure out when and how to best re-open our Sunday worship gatherings. In Ontario...we are not yet permitted to gather.
One person on the team believes that she is safe from spreading and getting Covid-19 if she wears just a clear face shield and no mouth/ nose mask. She volunteers at an organization that dries and bags food for developing countries and local needs. They only require the face shield therefore she is convinced that the shield is sufficient protection in both directions.
I cannot find any study in Canada or USA which explains the reasoning for your answer. Would you have something that i can pass along that would settle this matter so we can get on with further planning :)
This sure is an adventure!
"They provide protection from one thing: straight line droplet projection, to your eyes, nose, mouth, facial skin. Nothing else".....common sense, no? Oh, and partial, straight line droplet reduction FROM the wearer! Makes sense that maybe when doing materials handling tasks , you want to reduce emissions onto those items. But thats a very specific, narrow goal