What you pay
The Roomba j7 is $499, or about $899 for the j7+ with auto-empty; the Roborock S8 runs about $599–$779. Close enough that capability and support decide it.
Cleaning and navigation
The S8 adds a working sonic mop and LiDAR navigation that holds a more consistent path. The j7's camera is better at dodging pet messes.
Brand stability
iRobot's December 2025 bankruptcy filing leaves the j7's three-to-five-year support unclear, while Roborock is financially stable. The S8 is the lower-risk pick; the j7 mainly fits existing iRobot homes.