A fixed short visor can be a solid choice for gravel and commuter riding. It gives you basic sun shielding for early morning or late afternoon glare, and since it's short, it doesn't create the same aerodynamic drag as a larger mountain bike visor. You also don't have to worry about losing or forgetting a detachable piece.
The trade-off is that you can't take it off. If you ever want a clean profile for faster road rides, you're stuck with it. It also can't be adjusted up to accommodate goggles, so it's not ideal if you ride technical mountain bike trails. And while it helps with sun, it won't shield you from much rain or trail debris compared to a full MTB visor.
If your riding stays mostly on gravel roads and bike paths, a fixed short visor keeps things simple and functional. But if you mix in road cycling or mountain biking, a removable visor gives you more flexibility.