We have discussed these in the past - and leaving aside legality - they are considered a major no-no!!! Hate them.
No need to advertize our carry - and we have a permit to show if needed. A badge IMO could all too easily represent impersonation of LE - however pretty and despite what it says.
Legal? Depends where you are I guess but I doubt any LEO ever wants to see one! We'd possibly put a wearer of one in the ''macho/wannabee'' category!