Read from the World of Warcraft client build files.
How Riou's Vigilant Leggings Compares
Who It Suits
Leather is the armor type Demon Hunter, Druid, Monk and Rogue wear. With Agility or Intellect, Riou's Vigilant Leggings suits Assassination, Outlaw and Subtlety Rogue; Brewmaster, Mistweaver and Windwalker Monk; Balance, Feral, Guardian and Restoration Druid; Havoc, Vengeance and Devourer Demon Hunter.
Transmog Sets
Riou's Vigilant Leggings is part of the transmog set Barbed Assassin Battlegear (Rogue only). The other 16 pieces:
Built from the World of Warcraft client build files and recorded Auction House snapshots.
Where Riou's Vigilant Leggings Fits
Other Items Named Riou's Vigilant Leggings
6 other items in the current build are also called Riou's Vigilant Leggings. Same-name entries are usually a different rank, faction, quest stage or reward track of the same object.
Blizzard numbers items as they are created, so the named items next to ID 105031 (105026 to 105036) were usually added in the same batch as Riou's Vigilant Leggings: the same quest line, zone, vendor or reward set.