Drivers with Tesla’s “full self-driving” software often don’t know what their cars will do next.

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.