How will you resolve a Tradecraft roll where the dice outcome gives you at least one net success, one comet, two banes and a chaos star?
I believe that in Hero's Call FFG suggests that the GM can use chaos stars as crossed swords. By that rule the GM could use the chaos star to cancel the success and the player would have to use the comet as a hammmer, so the result would be 1 hammer, 2 banes.
For narrative purposes this could mean that the character was doing a great job, almost creating a superior item, but at the last instant something went really wrong and it came out a poor quality item instead.
I often use chaos stars as crossed swords (or banes, whichever is worst for the character), it gives the chaos stars more versatility and puts them more on equal terms with the comets.