There are no visual differences between upgrades. However, the duration of the effect increases by one second each time the Shock Bomb is upgraded.
Shock Bombs are very similar to EMPs (ElectroMagnetic Pulses).
The Shock Launcher's munitions are very similar to the Shock Bomb, but unlike the Shock Bomb it can only shock troops even if other defenses are in its area of effect. Also, the Shock Launcher does a small amount of damage to your troops while the Shock Bomb does not do damage to shocked defenses or troops.
The Shock Mine's effect is also similar to the Shock Bomb. It activates when a troop steps on it. This triggers an explosion that does damage and stuns troops for a longer period of time than the Shock Launcher.