The two most popular defense shotgun chokes are the Open Cylinder (no choke at all) and the slightly choked Improved Cylinder.
In past years, the Open Cylinder was THE setup for defense guns, but in recent years more and more makers are going with the Improved Cylinder.
The Improved Cylinder is better for shooting slugs, and allows buckshot to keep a tighter pattern.
As Remington puts it on their Law Enforcement web site, they use the Improved Cylinder in Police guns for "Better pellet accountability".
Cutting off a shotgun barrel leaves it with a Open Cylinder, or no choke, that shoots both slugs and buckshot quite well, especially in actual home defense guns where you want as open a pattern as possible.
Cutting a barrel off is really not a big job, and most people can do an excellent job at home by using the right techniques.
The only problem is in getting a new front bead or sight replaced.
These days, it's much easier to find inexpensive short barrels, so in many cases, you're better off just buying a new or used 18" barrel, and selling the longer barrel or keeping it for hunting or clay pigeons.
