The service was very good. However, the return location was underground, and neither QEEQ nor the rental company mentioned this. I spent nearly an hour circling around Plaza de España and still couldn't find it. In the end, I had to park the car on the roadside and call their staff. They sent someone to pick me up, and that's how I finally found the place. But by then, I didn't have time to refuel the car, and I was fined 18 euros. The rental company staff also admitted that their return location is very hard to find, with only a small sign at the entrance of the underground parking. Moreover, there used to be two entrances, but now only one is open. They expressed their helplessness about the situation as well. You definitely can't find it just by using GPS. While I was handling the return procedures, several people called to ask how to get there.