A magazine disconnect is awful in competition as you cannot unload and show clear -- and then drop the hammer -- without reinserting a magazine first, which is a total hassle and has to be explained to the SOs each time. You've got to keep an extra, empty magazine on hand to do that with as no SO is going to let you insert a loaded mag after your "show clear" step. Just a pain in the butt. We do deal with it with the Hi-Powers and a few other guns that come with mag safeties, but it is awkward complexity for no good purpose.
As far as a loaded chamber flag? That's really just an eyesore more than anything else, but like any other mechanical device, the more moving parts, the more stuff there is to break or get fouled somehow.