M209dw and MFC-L6800DW share specifications such as Print Technology (Laser), Automatic Duplex Printing (Yes), USB (Yes), Ethernet (Yes).
The main differences: Printer Functions (M209dw: Print, MFC-L6800DW: Print, Scan, Copy, Fax); Black Print Speed A4 (M209dw: 29 ppm, MFC-L6800DW: 48 ppm); Print Resolution (M209dw: 600 x 600 dpi, MFC-L6800DW: 1200 x 1200 dpi).
M209dw may suit users who need its differing values, while MFC-L6800DW benefits those who need its paired strengths. Review the specs table above before deciding.