I had to try the Oliv G, just to find out about the gut sound on my bass. I am happy with Pirastro Evah Pirazzi strings so far, but the Oliv G has a lovely sound. It is as thick as a D string, but very easy to play. It seems to be responsive and more alive than other strings, although I cannot exactly say why I have this impression. The tone is full and rich, both pizzzicato and arco.
I took the bass to my luthier to attach it, as the grooves had to be widened. I would consider replacing the D string too, as there is a tonal difference between D and G, particularly on arco. It does require regular re-tuning, unlike the nylon strings which stay in tune for a week, but this was not a problem. The construction looks very good so far.
If you can afford the string, (yes, they aren't cheap), then give it a try!