At least you know what a firmware is
Bitsetting is when your drive burn a DVD+R or CD+R as a DVD-ROM disk, this mean the reader think it is reading a pressed disk instead of a writable one, this increase the amount of compatible reader, I think it is also mandatory for some type of copy.
DVD+R DL are already bitset automatically on the DVR-109, but buffalo add the same option for the Single layer disk.
Buffalo is a brand using the PIO as OEM, they have their own firmware numbered 8.17 and 8.40 compared to 1.17 and 1.40 on the standard pio.
AutoBitseting mean the option to bitset is not selectable, but aplied on each disk burned.
Have fun deciding!