We know that face-mask-shield don't protect against droplet nuclei which float in the air, so one could end up infected, with COVID-19, even when wearing them.
However the face-mask-shield plus a surgical mask leads to better protection.
Approximately, how much of protection? e.g. 50%, 70%, ?
Additionally, would the protection be improved by extending the borders of the face-mask-shield (the limit is up to the chin)? that is, if one glues a larger piece of plastic to the face-mask-shield?
For example these mask, is there a real difference among them regarding protection?