I use this wireless for both e-guitars and e-bass.
My only comparison is a cable connection, which is obviously better.
However the quality decrease is not noticable enough to discurage me from using it in a live environment. On the other hand I wouldn't recommend recording a song with it.
It has more problems with the bass sound that the guitar sound, but that seems to be an inherent issue with wireless devices (noticed the same in wireless IEM devices).
I haven't tested it for vocals, but I can imagine, that the decrease in audio quality is more noticable there, especially if used for lead vocals. But for that I would recommend an all in one wireless microphone anyway instead of a body pack solution.
For any tone purist that might not yet be convinced: If you don't have a really good sound guy in FoH then your tone won't be that great for the crowd anyway. In such situation, an engaging live performance and movement on the stage is much more memorable for the crowd than the audio quality increase you'd get with a cable connection.
Rating:
While I'm perfectly happy with this device I'm not giving it 5 stars, since I'm sure that there are better solutions out there. If there was a qualit / price ration ranking, that would be at 5 stars.