Fracture: 220 total potency. 100 slashing potency, 120 potency DoT
PLD 123: 150 slashing + 200 slashing + 260 slashing = 610 slashing potency, or 203.33 average per GCD

With Storm's Eye up, PLD's RoH combo is raised to approximately 225 potency per GCD. Also with Storm's Eye up, Fracture is raised to approximately 231 potency per GCD.

The difference is very small and certainly doesn't warrant regular use due to its TP cost. To use it or not during FoF is tricky ... if, say, you know you're going to get exactly 4 combos in your FoF, as you should without Selene, it's probably a DPS loss to use it since you're losing a RoH buffed in exchange for a Fracture buffed. If you have very high SS (for some reason) or Selene's buff active, and it'd turn into something where your final attack in FoF will be a Fast Blade, sure, go for it, you'll have a very realistic gain.