The first week I owned this, I came home four nights in a row and noticed the floors were clean. Not in the satisfying way where you can see the lines in the carpet. In the boring way where you forgot they needed cleaning, and they were already done. That is the entire pitch for a good robot vacuum and the j9+ is the first one I've owned that delivers it without a fight.
The dock is the part iRobot got the most right this generation. It looks like a low side table, not a piece of medical equipment, and it hides both the vacuum bag and the clean-water tank for the mop inside a single piece of furniture. The j9+ docks itself, empties its bin, refills its mop tank, and is ready for the next run, all without me opening anything. I change the dust bag about once every two months in a household with one shedding dog. The mop pad I rinse weekly.
The vacuum is good. Suction on hard floors and low-pile rugs is more than enough for daily-traffic dust, pet hair, and the cereal my nephew throws at the kitchen island. On mid-pile rugs it does a respectable job; on deep shag it gives up, which is fair. The j9's mapping is mature now: it learned my apartment layout in two runs, names rooms reasonably, and lets me send it to clean just the kitchen with one tap.
The mop is the surprise. Past iRobot mops were essentially a damp rag dragged behind a vacuum. The j9+ lifts the mop pad up and over carpeted areas, which sounds like a marketing slide and turns out to be the thing that makes the combined vacuum-and-mop actually usable. It mops the kitchen and the bathroom, lifts the pad, vacuums the bedroom rugs, and comes back. I no longer have to schedule mop runs separately or push it out of the rug.
Obstacle avoidance is the other thing that has gotten better in a way I notice. The j9+ has not eaten a charging cable, a shoe, or a sock since I got it. It refused to enter a room where I'd left a jacket on the floor, which I noticed only because the app told me. It also avoids dog accidents, which iRobot will guarantee in writing — that is not a feature you want to test on purpose, but it's the kind of feature that justifies the price after one missed cleanup.
The catches are the usual robot vacuum catches. The mop is not a deep clean; sticky spills still want a real mop with real cleaner. The j9+ does not handle dark or very thin rugs well — it sometimes mistakes them for cliffs. Setup of the no-go zones via the app requires patience and a couple of botched runs to learn. Battery is around 180 minutes, plenty for an apartment, less generous for a 3,000-square-foot house where you'll see it dock to recharge mid-run.
The price is the hard part. Around $1,000 puts the j9+ above most competitors and right on top of the Roborock S8 MaxV Ultra, which has lidar mapping, a more aggressive mop, and a dock that also washes its own pad. Roborock's mop is better. iRobot's obstacle avoidance and app are more polished. Pick your trade.
Verdict: Buy this if you want a vacuum-and-mop that disappears into your life and you'd rather pay for polish than for raw specs.