9mm AR's are the greatest thing for having indoor fun in the winter time. Be it a pisol as mentioned above or a rifle, you can shoot them on most handgun ranges so you can have as much indoor range fun as you want. The .223 you need to fire on a range approved for rifle calibers if you want to shoot it indoors. Not all clubs have this.
Don't forget, though... it is only a 9mm so don't expect the same accuracy as a .223 for distances past 100m. It's the round, not the gun.
My outdoor range is 1hr, 20min away so I don't get out there much. My indoor club with a rifle range is only 50m. So I end up shooting my 9mm a lot more on the handgun range in the winter time. If I'm going to risk road conditions to the outdoor range in the winter, I don't bother with the 9mm since I take the .223.