This movement addresses two things most people need to work on but dread doing: core stability and hip mobility.
The normal standing landmine is already a great exercise to work the rotary and lateral core, but doing it in the bottom of the squat increases the stability demands even further while also building stability in the pelvis and serving as one hell of a hip and groin stretch to boot.
In this exercise, the bar promotes a deeper stretch in the squat, but once you start moving your arms you must reflexively stabilize your hips and core to keep from shifting or swaying.
While these may look easy enough, they're actually very difficult, so be sure you've mastered regular landmines before trying them, and when you do, only move your arms as far as you can before you start to lose stability. You'll know exactly when you reach that point. It's very hard to cheat on this one, so when you're done, you're done, which keeps you honest and keeps you from hurting yourself.
If you don't have a specific device to anchor the barbell, simply put the barbell in a corner. Just be sure the walls aren't sheetrock; I've learned that lesson the hard way, and it ends with a hole in the wall.