DH is a Health &Safety inspector who feels strongly about home-made masks being futile!
A home-made face mask may prevent a reasonable proportion of aerosolised saliva droplets containing possibly millions of individual virus particles from spraying from your nose and mouth into the air and possibly then being inhaled by someone within 2m.
However, some virus-laden saliva droplets will still escape around the sides of the mask if it is not properly face-fitted (no gaps between mask and face, enough to leave a pressure mark and be uncomfortable) and/or you have facial hair (beard or stubble).
This means some saliva containing virus could land on the outside of a nearby person's home-made face mask and wait there until they remove the mask. Unless removal is done correctly according to clinical practice, they are very likely to contaminate themselves.
Alternatively virus will simply be breathed in by a person with an ill-fitting mask.
Also the material used for the home-made mask may be completely inadequate at stopping hardly any aerosolised particles from passing through. The more light that can pass through the material, the more likely it is to be ineffective.
Mask wearing can lead to becoming complacent and ignoring 2m social distancing, which is much more important and effective, along with
thorough, frequent hand washing.
So overall there is virtually no benefit in wearing a home made mask as it is not face-fitted and people don't know how to safely remove them!