The Centaur AA Mk. II Cruiser Tank is a relatively slow but lethally armed and fairly well armored AA tank. With twin 20mm Polsten guns, the Centaur is perfect for literally mowing down infantry and planes, serving as a hard counter to infantry (especially blobs) and even anti-tank guns. The guns can also penetrate light armor, making it very deadly verses light vehicles as well. However, it is very sluggish, just a hair faster than the mighty Tiger II, but enjoys good armor and same health as most other medium tanks.
Centaur works well as an early shock unit, when enemy has no resources for tank yet and you can utilize this advantage to take some territory back. While anti tank guns still pose threat, your own infantry and firepower of centaur itself should be sufficent dealing with that threat. However buying centaur means you must rely on your 6 pounder anti tank guns dealing with armor as you most likely can't buy tank that is able to fight off enemy vehicles right away.
Centaur also works well as bit late addition to your armored forces if enemy continues heavy infantry play or enemy air strikes are constant.
With hammer tactics, you can via royal engineer repairing install emergency war speed to centaur for short movement boost. As centaur is slow and easily being chased down and killed by enemy tanks, emergency war speed gives centaur a way to get away from trouble. This isn't however excuse to leave it unsupported.