I HAVE TWO ROBOTS that clean the floors in my apartment: the Evolution Robotics Mint and the iRobot Roomba 530. The Mint sweeps and mops. The Roomba vacuums. Total retail cost for my live-in cleaning staff: $500.The point of deploying these devices is to save time. In practice, though, I don’t end up with as much free time as you would think, mainly because I find it impossible not to watch the robots work.

It’s like hiring someone to mow your lawn, then sitting down and watching him mow your lawn. True, the novelty wears off after a few months, but I still find myself curious. Will the robot pick up that huge dust bunny that would take me five seconds to pick up and throw away? Let me wait 10 minutes and find out.As domestic help, robots have flaws.

I bought my Roomba about three years ago; the Mint joined it a year later. But my dream of an immaculate, machine-cleaned home has yet to materialize—they can be slow and you have to space out your furniture to give them room to maneuver. But they earn their keep in other ways: They’re entertaining—a cross between the Three Stooges and a geeky Discovery Channel reality show. I’ve read that owners often grow attached to their machines. Some give their vacuums names; there’s even a website that sells clothing for Roombas.

My bots and I don’t have that type of relationship. And yet when a friend asks if I’ve ever deployed both at the same time just to see what would happen, I bristle. That would be immoral—like running a cockfighting ring. Besides, it’d be boring. When they bump into something, they just turn around and head the other way.

Mint Cleaner

The Mint is the newer kid on the block. It was released about two years ago; a more powerful model geared for larger spaces—the MintPlus ($300)—was released last fall. The creative team behind Mint includes designer Yves Behar and usability guru Don Norman, who coined the term “user experience” in the early ’90s when he worked at Apple. They’re a sort of dream team as far as consumer products go. The Mint is small, quiet, and inconspicuous—a sleek white box that looks like a character from “WALL-E.” It cleans only hard-surface floors (no carpets). I deploy it compulsively—sometimes more than once a day—because it’s so easy to maintain: Just swap out the reusable microfiber or disposable Swiffer cloth that is clamped to the bottom. The Mint has shown me how perpetually dirty my floors are.

The Roomba, first released in 2002, is the pioneer of cleaning robots. The latest model, the Roomba 780 ($600) is the sixth generation in the line (it does everything mine can, but more effectively and efficiently). Roombas have military roots. To figure out how to cover a room most thoroughly, it uses software derived from a minesweeping robot commissioned by the Navy’s Naval Explosive Ordnance Disposal Technology Division.

But the way it bounces around the room is hard to make sense of. Why do I feel deflated when it misses a scrap of paper just out of its path, even though I know it’ll make good on a subsequent  pass I am told there’s a method to its madness. All those bonks let it estimate the size of the room so it can adjust its running time accordingly. It can even tell when it’s hit a particularly dirty spot: A microphone listens for that clickety sound that’s so satisfying to hear when you vacuum.

Still, despite all the brain power behind the Roomba and the Mint, watching them work you can’t help feeling that you’ve just unleashed the dumbest things in the world in your living room. Cute, but stupid.

iRobot Roomba 530

Granted, “stupid” is the state of robotics. We’re a long way off from C-3PO with a feather duster. According to Evolution Robotics’ chief executive, Paolo Pirjanian, who oversaw the development of Mint’s software algorithms, tasks that come easiest to humans tend to be the most difficult for robots. Take traveling from point A to point B, so a robot can deliver a glass from the kitchen to the dining table: Once it sets out, the robot can try to figure out its position by counting the number of times its wheels have rotated. But if the wheels slip, the robot gets hopelessly lost. Mint’s solution is a cube that projects infrared spots onto the ceiling, which the robot uses to pinpoint its location.

And these robots work more slowly than you or I would. A human wielding a broom and dustpan can be shockingly efficient. I’ve clocked it: In my modestly sized rooms, the time it takes to prepare, deploy and clean the robots isn’t much less than what it takes to vacuum or sweep.

Despite this, the Roomba and Mint grow on you—as they were designed to. With the Mint, Mr. Norman suggested giving the device cues (chipper sounds, flashing lights) to make it seem like a pet that loves doing chores. Both devices play a short tune when they set out to work. The Mint’s is an ascending minor scale—a choice I don’t understand, as it sounds slightly ominous. The Roomba’s tune is heroic, John Phillips Sousa, a battle charge, which seems appropriate.

Efficiency, I’ve come to realize, is beside the point. There’s a joy from watching something undertake a task that’s challenging for it but easy for you. It’s the opposite of watching pro sports. The best analogy I can think of is watching your toddler struggle to crawl up stairs or climb onto the couch. You root for your kid. You take pride in her simple accomplishments. Her foibles are endearing.

And that’s why when your robot finally finds its way to a dust bunny and swallows it whole, you stand up and cheer.