TF is worth 0.10 echo; you can cash it out for economy items at that rate later on in the event. Rat Market items can be acquired throughout the 3-month season every year, unlike event items, which have a much shorter window. Also, 3 out of 4 of the Rat Market items are strict best-in-slot, or only share best in slot with soft Fate-locked event items (Whitsun, Summer) or Ambition items.