We've had an iRobot Roomba 980 since Sept 2016 and like it very much.
Initially, we ran it a couple of times per week (scheduled within app) and then as your floors get cleaner from consistent regular cleaning, we've been able to do it once per week. You can tell the job by how full the bin is and the filter. Runtimes are consistent. It does have some 'boost' option when it detects more dirt in an area and stays there longer.
I take it upstairs about 1/4th the time.
Very cool! I just got a Roomba 981 on the Amazon Treasure Truck deal this week. It arrived yesterday and has been charging, so I get to try it for the first time today.