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The Zwift Cog + Click is a 14 tooth single-speed cog, compatible with almost any 8-12 speed bike and a two button digital remote that’s easy to attach to wherever you’d like on your handlebars, that offers 24 virtual gears of resistance when used with Zwift. The Zwift Click’s virtual shifting functionality only works on the Zwift platform.
If you have no intention of using Zwift, then a cassette that matches your drivetrain may be a better choice.
If you plan to do all your riding in Zwift, the Zwift Click will allow you to shift virtually and the single speed Cog will be perfectly suitable for ERG mode workouts.