Shotguns give you instant damage output at extreme close range fairly quickly, with good flexibility in terms of how you engage within that range. Because of this simplicity, speed, and flexibility, they are the favorite choice among PvP-ers. Fusions stretch that range out 3-4 times and have overall less spread. Lower Impact models offer an experience closer to a shotgun with restrictions to your reach to match (both in the way of the extra bolts and the limited range stats). Where higher impact models offer up more reach and less bolts being required to kill in return for lo-blam!- charge times. Fusions are like primaries in that they have an actual time to kill. But because the extreme vast majority of that TTK is through a delayed trigger, you can front-load that before an engagement. Fusions are also less mobile due to FAR greater penalties to accuracy in the air and while sliding (via the stability reduction), and the charge time with multiple telegraphs of your planning can make them play predictable, in the sense that they are a very flow-chart type of weapon.