The new Blade Flurry that's on the PTR is by far the most exciting update for combat rogues in at least a year. The current version, which still isn't finalized, allows 40% of our melee damage to be cleaved onto up to 4 targets at once. It's a significant step up from the old Blade Flurry when we're facing a handful of targets, but what about in a regular cleaving situation?
In order to do the math for Blade Flurry, you have to figure out what you're gaining and what you're giving up by activating it. Blade Flurry increases our melee damage by 40% per target, but not all of our attacks are replicated. Our autoattacks, Shadow Blades, Main Gauche, and most of our other abilities are all affected by Blade Flurry. Notably, BF doesn't apply to Deadly Poison or Rupture. While many combat rogues are ignoring Rupture today, it will likely be worth using once we have our 2-piece tier 15 bonus, which extends its duration.