Booked this activity last minute, while at the rental location. The vehicle we got was noisy, slow, and very beat up. We saw many newer vehicles around town that were rented from the other locations (we got ours at Union Square).
Putting all of that aside.... you MUST do this if in town. You will have a fantastic time and be able to see all of the sights that you CANNOT actually see on the hop-on, hop-off buses. We spent about four hours and were able to head up to Coit Tower and Telegraph Hill, up to Inspiration Point, Twin Peaks, North Beach, the Painted Ladies, drove down Lombard and had more people taking OUR picture than pictures of the street... we will certainly do this again when we are able to get back to San Francisco. We'll also look for Go Cars in other cities we visit; we'll just make sure we get one that's in better shape.