Makes swapping between my 5D and 7D a bit tricky on occasion. I've shot outside in very bright sunshine at ASA 400 without meaning to.
I only use 400 in my film cameras by default
Never using auto ISO, except objects or me moving sun-shadow.
Majority if my shots:
Start with as low as possible ISO.
Select aperture I want.
Check shutter speed I need.
Check to have correct exposure.
Adjust ISO if current one doesn't provide right exposure with selected aperture and needed shutter speed.
Works well with AV and M, flash or not.