As I said earlier - I will be wearing a mask now that they're mandatory. BUT... some of the replies on here really highlight the key issue with them. Masks are to protect other people from you, if you have the virus. If you do what people say on here 'take it off, put it in your bag, put it back on again... use it again later' and so on, all that handling of the mask means that if you have the virus you will have it on your hands and therefore onto everything you touch. People will not be sanitising their hands every time they touch their mask. If you don't have the virus, it doesn't matter if you touch it/other things or not... but then if you don't have the virus, wearing a mask makes no difference anyway!
Right at the start of lockdown, there was a suggestion that we should all 'behave as if we have the virus' (or something like that) - ie: making you really think about how your behaviour or actions impacted others. That's what should happen with masks, but it wont. Thankfully there is very little virus around in the wider population, so for most people who aren't using their masks correctly, it won't matter. But they have real potential to become 'vectors of disease' (to coin one of BJ's phrases).
I will comply, and I will wear one (and all the masks I'll be making each have their own pouch to go in my handbag, and into the wash, and I'll take several with me whenever I leave, so I have have a clean one after I've taken the previous one off). We won't see any affect on the numbers, because they're at low levels now and with lockdown relaxed (and plenty of testing), we'll see case numbers in the hundreds for some time to come regardless of mask wearing (the number of cases picked up because of interactions in shops must be tiny). But hey ho, it is what it is...
Conversely, I think masks on public transport makes more sense - people potentially in close proximity with each other for a prolonged period, and a more simple case of 'put mask on, get on train/bus, carry out journey, get off train/bus, put mask away' means the mask has a stronger purpose and is much less likely to become a virus spreader. So I'm not 'anti-mask', but I think it's about the context and situation.