For the USMLE, sure it is low yield but since most of what they want to ask is barely mentioned in First Aid I think this is another way the test takers "set us apart" from our MD counterparts.
Not sure about micro made ricidulous, I never opened anything but FA. Botulism, Ricin, Variola, ANTHRAX, is enough to get your through. Luckily my micro background was strong enough pull me through most of the BS portions of micro on this test.