Yes — collecting all chests unlocks the trophy/achievement and gives you enough resources to fully upgrade Evie’s Fear skill tree , plus the final piece of the “Lady’s Legacy” outfit (no statistical bonus, but looks great in cutscenes).
Once you have 4 keys, start opening chests. If a chest is guarded by a "Terror" zone, use the Volatile Knife (Upgrade Evie’s Fear skill tree first). Throw it into a group of enemies to make them flee, giving you a 10-second window to pick the lock. Assassin-s Creed Syndicate Jack The Ripper Chests Map
The Jack the Ripper DLC for Assassin’s Creed Syndicate is a masterful shift in tone. Swapping Evie Frye’s calculated stealth for the visceral terror of Whitechapel’s most infamous serial killer, the expansion introduces a dark, claustrophobic version of London. Among its most challenging collectibles are the (often simply called "Jack the Ripper Chests"). Yes — collecting all chests unlocks the trophy/achievement