They are good for lazy surface cleaning but given the form factor, they’ll never have the cleaning power of the Dyson.
But the kitchen/dining area also has cords, chairs, and (under normal circumstances) various things being packed/unpacked in various corners. My compromise a couple years ago was to get a Dyson which is super-quick to whip out and spend a few minutes doing a rough vacuum. MUCH easier than to haul out my old canister vac. And probably less effort than keeping things iRobot ready and emptying it.
I have both kids and a dog, so the daily cleaning my Roomba does is a game changer. No more piles of fur or crumbs accumulating in the corners. I have to empty the bin every other day, but it takes me less time to do that than it would to manually vacuum the main traffic areas in the house once or twice a week.
Personally, I like the fact that the Roomba forces me to keep wires and other stuff of the floor. I think it makes my house appear less cluttered overall, but it's a matter of opinion.
I actually have a cordless Dyson too, which I think complements the Roomba well. I use it to occasionally deep clean a couple of area rugs.
Since buying the roomba I've not used the real vacuum cleaner at all, although I still mop the floors once every 7-10 days which is mostly necessary because of the child we have running around the place.