Not all BIOS give you that option to choose which drive to boot from like that. I know my BIOS doesnt. I would haev to shut off one of my SATA HDD's to be able to do that trick. But since all my drives are partitioned and i have stuff located on each drive i need doing that isnt a option.
The F12 is a good thing. At times. I have found the boot loaders much easier that way if i forget when or if i happen to miss hitting F12 at the right time the loader makes it easier. Plus i haev my time limit set to 5 seconds so it doesnt stay up long.