There will always be good and bad instructors, just as you would get in any profession. I have had brilliant ones and not so brilliant, I have only ever ditched one instructor who whilst being an excellent pilot his instructional skills were a bit lame.
My view is that if an FI shows you another of doing something (such as downwind checks), then listen and see what you think. Some you will swap to and others you will dismiss, there is more than one way to skin a cat and they may have a better way than your adequate way!
I wouldnt tell them to shut up straight away - unless of course they are being a pompous @rse then just decide nod and get the hour over and done with so you go off on your own.
J.