We decided to take a tour with GoCar since it was advertised as a convenient way to see a range of landmarks through a guided tour. However, we were very disappointed.
The GPS system they use (their own) is horribly misguiding; the navigation icon does not rotate, meaning that it does not show you which direction you are going, until the map moves and you realise that you've missed your turn or have gone the opposite direction.
There was also a supposed to be voice guidance to complement the navigation screen, which the shop assistant informed us was at full volume before we left the shop. However, this was inaudible even when we were waiting in traffic, let alone driving the car's loud engine.
We basically spent the entire trip trying to figure out for ourselves where we were going, wasting a lot of time in the process, since their was no guidance from the GPS system whatsoever.
We eventually managed to get back to the shop thanks to a function which guides you back to the shop (which funnily enough actually works properly, since it runs on Google Maps). We raised our complaint to the staff, who did not take it well. Rather than addressing the utterly poor navigation system, the guy in charge said that we should have called them during the trip.
Despite explaining that we could not do so since we were driving and we couldn't find anywhere to park legally, he simply kept on repeating the same thing and actually said that this was "our problem". I still could not understand how he proposed to help us should we have called, since he acknowledged that the system was designed that way and that it was working as intended.
Considering that the main users of this service are tourists (who would be unfamiliar with the streets of Barcelona), one would expect a decent GPS system and that the service providers would understand this. However, this was not the case.
We realised that the representative was not interested in customer satisfaction, but rather in holding onto profits. Definitely would not recommend; better to just rent a car.