One thing to remember is that face shields aren't as effective at stopping exhaled droplets getting into the surroundings as masks (nor them getting inside you) so if you can wear a mask that is the best option. I did read that the Scottish Government were considering not recognising face shields as an acceptable face covering but aren't sure whether or not that was pursued.
Hi
Current ScotGov position on face coverings/shields can be found here:
https://www.gov.scot/publications/coronavirus-covid-19-phase-3-staying-safe-and-protecting-others/pages/face-coverings/
In case that doesn't work, or you don't like following links from people you don't know, the most relevant bit is:
What is a face covering?A face covering can be a covering of any type, except a face shield, that covers the mouth and nose. It is recommended that it be made of cloth or other textiles and should be two, and preferably three layers thick, and through which you can breathe. Religious face coverings that cover the mouth and the nose count as face coverings for these purposes. Transparent face coverings which assist communication for those who rely on lip reading and facial expressions can also be worn.
Face shields may be used, but only if they are worn in addition to a face covering underneath, as the evidence shows that they do not provide adequate protection.
If you are unable to wear a face covering, a face visor or face shield can be worn as it does provide a limited level of protection.There's a lot more, including examples of thing that aren't masks, warnings that they're not a substitute for everything else (and what 'everything else' is!), how to reuse/dispose of them and a video demo of how to construct a face masks which looks interesting, simple and quick to do. But this is probably more than enough!
HTH