the Rapier is super great at dealing horrifically massive damage to anything you can get close to, it's fantastic for mowing down hordes of bugs but it's also great as a boss-buster for anything ground-based, and it can chew through armor and stagger a lot of resilient baddies. and since it has its own clip battery it's also a fantastic last-resort weapon if your jetpack runs out of juice.

the Stardust Cannon deals horrific damage at genuinely longer distances than it has any right to and is great for kiting and splashing large groups of dudes but also fantastic for doing large numbers to boss monsters, esp if they move too fast for the slower moving plasma cannons. and it costs way less than most plasma weapons too! also if you suck at aiming the spray'n'pay really works out :)

and the gleipnir homing grenade thing spits out 600 homing projectiles that are fantastic for downing mob fliers and staggers almost anything it hits, so even if it's low damage it's a great offensive decoy you can bust out after a hit-and-run on a transport ship or teleportation anchor that will help keep you alive as you dash back off to safe kiting distance.

having all three on hand allows for some truly YEEHAW carefree grade S+ wing diver bullshit and I absolutely love it