Q: How does this compare to coilovers for lowering the car?

Different tools for different cars. Coilovers replace the suspension outright and suit platforms without air; this kit is the right answer for the air-equipped Model X because it keeps the factory system, its auto-leveling, and its raise function intact. You get a lower stance and the handling benefit without giving up the convenience air suspension was built for. For an air-sprung SUV, that trade-off is the whole appeal.