Lego: about as devastating as you think it would be. Not as good as lead but you won’t see any volunteers raising their hands to evaluate its effects downrange in person.
Pretty much anything can be dangerous when you power it down a shotgun barrel after packing it into a shot cup. Hell, an empty shot cup can hurt someone by itself.
FYI the plural of Lego isn’t Lego, Legos or anything like that. It’s L — connection timed out.