M1120 and DCP-L5650DN share specifications such as Printer Functions (Print, Scan, Copy), Print Technology (Laser), USB (Yes), Product Type (Monochrome Laser Multifunction Printer).
The main differences: Black Print Speed A4 (M1120: 19 ppm, DCP-L5650DN: 42 ppm); Print Resolution (M1120: 600 x 600 dpi, DCP-L5650DN: 1200 x 1200 dpi); Automatic Duplex Printing (M1120: —, DCP-L5650DN: Yes).
M1120 may suit users who need its differing values, while DCP-L5650DN benefits those who need its paired strengths. Review the specs table above before deciding.