back price and stats
i think it is more for cosmetic looks. the backpack (which i own) can show your guild’s emblem on it for easy identification. the back brace does not.
it may also be simply: it’s a guild-based item. if you like your guild and want to represent it around Tyria, it’s nice flair to have. rings you cannot see anyways, but don’t actively show your affiliation (because you cannot see them).