Many shotgun makers, including Remington are now using the Improved Cylinder for buckshot and slugs.
Remington uses the Improved Cylinder on their Police guns, because they say it shoots tighter buckshot patterns and slug groups than the Cylinder bore they used to use.
What's important is to actually shoot a variety of shells at a patterning board to determine what works best in your specific gun.
Remember, for actual HD (Inside the home) shotguns you may not want a tighter pattern.
The typical house has a maximum distance possible of around 30 feet, an apartment around 20 feet.
A good rule of thumb on shotguns is: The shot will spread "About" 1 inch per yard.
In other words at 6 yards (18 feet) you'll get a circle about 6-7 inches in diameter.
That's not that big.
In my case, since my 870 Police is a REAL HD Inside the house gun, I opened the choke from Improved Cylinder to an actual straight Cylinder bore.
I want a more open spread, not a tighter pattern.