The Argon ONE M.2 case features all the high-end features of the Argon ONE Raspberry Pi case but with the added feature of an M.2 interface for using M.2 (Key-B or Key-B&M) SATA solid state drives (not included). It also includes some updates over the previous generation of the Argon ONE case including full-sized HDMI ports, power management modes, and built in IR support for using the Pi with remotes. Unfortunately the M.2 SATA support does come at the expense of the USB 3 ports, but offers a great option for those looking to use the Raspberry Pi 4 with high capacity memory; uses such as media centers.
As mentioned above it includes all the features of the Argon ONE case. In addition to providing passive and active cooling to keep the Pi 4 running cool, it incorporates multiple pieces to allow for access to different levels of the board like a magnetic dedicated door for the 40 pin connector that provides pin numbers and labels. An included fan HAT provides software controllable, active cooling while the aluminum enclosure provides passive cooling through two extrusions that provide a heat sink for the ICs on board (thermal tape included). An additional interface board plugs into the Pi and redirects all the connectors (outside of the 40 pin) to the one side of the enclosure. But probably the best feature is a properly configured power button that provides the ability to safely shutdown, reboot, or force shutdown the Pi.