The first is the 2150cd/cdn color laser for $349, or $399 with the duplex printing option.
The MFP version is the 2155cd/cdn, with the additional scanner, copy, and fax capacity, and the network interface is Gigabit Ethernet. It costs $549, or $649 for the duplex version.
Both use a system that Dell calls Emulsion Aggregation Technology, which basically means they use smaller toner particles. Dell says this allows smaller pixels which should result in smoother images, but the resolution is still stated as 600 dpi, which is pretty much standard for laser printers in class. Dell also states that the smaller toner particles demand less energy during the warm-up and printing process.
Both tout a cost per page of 2.4 cents for black and white, or 14.3 cents per color. Both have a one-year warranty, and Dell offers an "advance" exchange service, meaning they will send out a replacement without waiting for the defunct unit to arrive back at Dell's facility.
As usual with most Dell products, you have to buy them through Dell, but replacement toner cartridges should be available locally.