I like to use CJS on maps where neither heavy splatling or charger perform at its respective peak performance. An example could be Blackbelly Skatepark. Although charger and heavy can work on this map, CJS is the standard backline pick.
With this gear I aim to throw my burst bombs pretty far to weak foes or finish off already beaten foes. The MPU is used to barely increase the effective range of CJS. It's not much (iirc), but I see a difference. The rest of my abilities are self-explanatory.