Just curious...
'If' the brass rivets are more difficult to work with, assuming one is trying to pound it through then lock in the keeper piece, wouldn't it work out to make a smaller hole first with a punch or suchlike then install the sized brass rivet keeper into that hole? Hope it makes sense, sounds feasible and less likely to tear, etc., maybe not, I dunno.
Just a thought anyway.
'Ol Gabe