If you have ever flushed up a grouse and walked in after it into some bush, you will understand that the short barrel is a real advantage as you don't find yourself swinging into trees. Try it sometime the 18' barrel is great as the radius is greatly reduced in thick brush.
But before you get all excited about buying a gun just to see that you like it. Buy a used regular barrel and cut it down. All you need is a hacksaw and it still remains legal. There are a lot of optional sites availible to install.
I can't beleive what a spare barrel is worth from remmington for the 870. I think it's highway robbery.
Cheers