The idea is that the mouth covering restricts the transfer of CV by catching it in the covering. So that means there is likely to be a build up in that face covering.
Yes, but it will be your breath that is trapped inside the mask, so you will only be giving it to yourself!
If two people meet each other and both are wearing masks, there can't be any transmission on to each others masks, as there are no droplets escaping from the masks....