Goth, Jabo is referring me being Jedipedia (don't know where that comes from)
German cluster munitions (prefix AB-) are fairly useful against tanks, but more so against parked aircraft and vehicles. They are slightly difficult to use in Il2, with it being slightly difficult to calculate the impact point. With a unitary warhead, as we know, it is rather straight-forward. You release the bomb and it follows a projectile motion, which with a bit of practice can be applied with a fair degree of success. However, the problem with the cluster munitions is that they burst about a second after dropping from the rail (assuming no bomb delay set in the arming screen) and thereby produce a swarm of tiny bomblets that will shower the target. While this in theory sounds easy enough, in practice it proves slightly more challenging.
The most common approach seen in flying il2 when dropping bombs is a form of glide bombing, but with a relatively low dive-angle (about 20-30 degrees) and the low altitude of the approach. This is fine when dropping HE or general purpose bombs (it really isn't but this is where the 2-seconds fuse whining comes from, unless you are packing Mk82 snake-eyes or something), however cluster munitions need altitude and time to deploy properly.
The capsule (container) opens after about a second and distributes the bomblets, this requires at least 3-4 seconds of flight for the bomb to establish a decent deployment pattern. The longer the canister has been opened, the larger the pattern. Too short a flight and you get a very concentrated burst, too long a flight and all you get as a few 1kg bomblets spread over a large area, which will not yield very good results.
My suggestion is to dive in at about 700-1000 meters AGL (2500-3000ft) and dive in at about 60-70 degrees. Keep the target area in your gun-sight and when it passed below the reticule, drop the bomb (this will be at about 3-400 meters AGL). The bomb being its projectile motion and deploy its contents within a few seconds, thereby giving it ample time to get a decent area of effect. Practice against a variety of targets and after a while you should develop a feel for how the bomblets spread and at what altitude to drop the bombs for various types and layouts of targets.
A single AB250 or AB500 can be rather weak, so do not expect them to be nearly as effective as a modern (post 1960s) cluster bomb. They can be very good weapons with a bit of practice, however Il2 does not model smaller amounts of explosives very well. Most targets are better prosecuted with SC250 or 500 with HE unitary warheads.
They can be quite a bit of fun though, and with practice and experience can be effectively deployed against soft-skinned vehicles and parked aircraft with a high degree of success.