Mechanical disc brakes use a traditional cable to squeeze the brake caliper, similar to how rim brakes work but with a disc rotor at the hub. They're typically found on entry-level road bikes and offer a real step up from rim brakes in wet weather—something commuters and all-weather riders will appreciate right away.
However, they don't match the feel or performance of hydraulic disc brakes, which use fluid pressure for smoother, more precise stopping (called modulation). Mechanical discs can also be finicky to keep both pads contacting the rotor evenly, requiring more frequent adjustments.
Mechanical disc makes sense if you're on a tight budget and want disc brake benefits like wet-weather reliability and wider tire clearance. But if you can stretch your budget to a bike with hydraulic discs, the improved braking feel and lower maintenance are absolutely worth it—especially for faster riding or hilly routes.