I breastfed twins for 18 months.
Feeding two babies takes a while and is more noticeable than feeding one (largely because twin babies draw attention anyway).
I never used a cover and I never had any negative comments.
As a PP said most people don’t notice and those that do largely don’t care.
I had regularly supportive smiles from other parents (Mums and Dads), occasional offers of water or tea from cafe/restaurant staff and a few lovely supportive chats with very elderly ladies telling me I was a wonderful mother. .
I never, ever had negative comments or nasty looks.
Occasionally surprised looks when they realised what we were doing but not nasty.
Again, like others I fed everywhere, parks, offices, shopping centres, cinemas, cafes, restaurants, baby groups, family parties and churches.
Nearly all my friends breastfed too and none of them experienced any unpleasant situations either.