A regular front diff with light fluid(3000) in the front gives alot of off power/ turn in steering. a regular front diff with thick fluid (7000)can give you alot of steering and stability on power/turn out.
An Active diff or Smart diff acts like a light weight fluid on turnin and binds up and acts like a diff with thicker fluid on turnout.
Best of both worlds except The front smart/active diffs don't like off camber turns or grippy indoor blu groove or grass/astroturf.
The center is trickier. Off power its loose to free up the drivetrain for better steering. On power it stiffens up and is good for on power steering. But it can make the car hard to drive by sending too much power to the rear tires. It increases acceleration and feels grippy on the straights. Best on high speed flowing tracks or tracks with alot of grip. Can screw up your brake bias on a slick track.
I think having both front and center active/smart diffs is a great tuning tool, but they won't allways make the car faster or easy to drive.
I plan on running one in the front alot, not so often in the center.