I have up until recently had Monofilament fishing line strings on my "sono-tube banjo. I just wanted to see if there would be an improvement in sound quality if I used the NylGut strings. I ordered some Nylguts and installed them and after they settled in I was very favorably impressed with the improvement in the sound.
They are Louder (a lot) which is a good thing in this case. And I'd call it Mellower (is that a real word?)
I realize that describing a sound with words is like trying to nail Jelly to the wall, but that's about as close as I can describe it.
The sono-tube banjo now has a wooden top (3/32") Baltic Birch. and with the monofilament line it was quiet but not unpleasantly so. It sounded like one of the "Back Yard" banjo kit banjos that are available online. Now with the Nylgut strings it sounds like a regular minstrel banjo (the ones in videos on this site).
The 4th string really BOOMS and the other strings have a lot better sound too. I have it tuned dGDF#A
its a lot more fun now that it sounds like it's supposed to.