Tesla owners have been wowed by their cars’ new abilities, but some say they have also been alarmed and frustrated by the accompanying flaws. One second drivers find themselves praising the cars’ skills; the next moment they’re grabbing the wheel to avoid crashing or breaking the law.

“Full self-driving” is a suite of driver-assist features that Tesla hopes can one day enable cars to drive themselves. (It’s not fully autonomous today, but that hasn’t stopped Tesla from calling it “full self-driving,” which has angered some self-driving experts.) Other automakers like Mercedes-Benz, GM, Ford and Volvo offer cars with similar features that may change lanes, parallel park, identify speed limit signs and brake for pedestrians. But Tesla has gone further with “full self-driving,” theoretically enabling people to plug in a destination and have the car drive them there. Tesla CEO Elon Musk has spoken of cars in the future driving themselves across the country, and traffic fatalities possibly being reduced by 99%.

But the company has only managed to slowly roll out “full self-driving” to roughly a thousand “beta testers,” who are still required to occasionally intervene. Meanwhile the cost of the “full self-driving” option has risen to $10,000. And while the feature is a major step, it still has major issues. Last week Tesla recalled a version of “full self-driving” within hours of its release because drivers were reporting false forward-collision warnings and automatic emergency braking. The issue was addressed in a new version released the next day. Tesla owners said they were impressed how quickly the company responded.

“It drove like a 9-year-old who had only driven in [Grand Theft Auto] before, and got behind the wheel,” said John Bernal, who owns a Tesla Model 3, of when he first got “full self-driving” early this year. “Now I feel like I’m driving with my grandma. Sometimes it might make a mistake, like, ‘no grandma, that’s a one-way, sorry.'”

Tesla did not respond to a request for comment and generally does not engage with the professional news media. It warns drivers that the technology “may do the wrong thing at the worst time, so you must always keep your hands on the wheel and pay extra attention to the road.” Drivers are told to be prepared to act immediately, especially around blind corners, intersections and narrow situations.

Some Tesla drivers say they’re concerned the feature’s inconsistent behavior is sometimes annoying and rude for other drivers. Videos posted online show it’s common for cars in “full self-driving” to drive down the middle of unmarked residential streets, in no apparent rush to move over for traffic coming towards it.

The cars also appear to befuddle drivers in other situations, such as being slow to take its turn at a four-way stop.

Kim Paquette, one of the first non-Tesla employees to test “full self-driving” when it was rolled out to a select group a year ago, says she uses the feature for nearly all of her driving in her Tesla Model 3. She was frustrated when she recently had to drive a loaner car that didn’t have the technology she’s grown used to. Paquette said she can sometimes drive the 85 miles from her home to her job at Boston’s airport without having to intervene because the car made a mistake.

Paquette can type an address into the screen on her Model 3, or hit a button and use Tesla’s voice recognition to tell the car her destination. Then she pulls down twice on a stalk on the steering wheel to activate “full self-driving.” The car lets out a chime, a blue steering wheel logo lights up on her screen, and the car starts taking her where she wants to go.

In some ways a system like this can seem like magic. But that magic is still flawed in both minor and serious ways.

Paquette has been frustrated, for instance, with her car’s tendency to drive in the parking lane on one-way streets in Newport, Rhode Island, where she lives.

But in most cases it is overly cautious around pedestrians, drivers say. Paquette recalled a recent drive in which she was cruising down a street as a person got out of a parked car. Paquette said her car stopped four car lengths behind the parked vehicle and exiting driver. To Paquette, it seemed clear the person exiting their car was going to walk to the adjacent sidewalk, rather than cross in front of her. The car could be cautious without leaving such a large gap, she felt.

She’s noticed that “full self-driving” struggles to sense social cues, including being waved through a four-way stop by another driver, or knowing what a pedestrian will do next. Paquette said she regularly takes manual control of the car to prevent it from making the wrong decision or irritating other drivers.

“If someone is standing on the corner, are they just standing on the corner or waiting to cross the street?” she said. “It’s a student driver for sure. It’s like teaching a 15-year-old.”

Tesla isn’t alone in struggling to get its cars to recognize social cues. Machines work best in predictable environments that lack complexity, and this has been a challenge for all autonomous vehicle developers.