Somebody may, on the surface, think that these shirts are fun and entertaining.
Yes, there are several that are innocuous enough.
But anything from that site that announces to the world that you are (or might be) carrying a concealed weapon is an incredibly bad idea for daily wear around the office, around town, or pretty much anywhere other unfamiliar people may be.
It will very, very likely put put the wrong sort of people on defense. The sort of cowardly people who, through their own ignorance, will turn to offense by calling people with more guns (but also badges) out to have a chat with you about the non-verbal violent threat that you just intentionally lobbed across a crowded restaurant.
Remember: concealed means concealed.