I got this so I can practice in silence while using my pedalboard, and also to use it as a stand-in for other effects (phaser, delay, etc.). It sounds very good, although it doesn't like having distortion or hard overdrives in front of it. I have the VS Audio Royal Flush, and if I have both sides on (stacked overdrives), the GP-50 "farts"—though that might just be my headphones. The Tone Snaps are very good and sound quite "natural," but you can still tell it’s not the real thing (which is okay, considering you're only paying 120 Euro).
Side note: I might replace my Hall of Fame 2 and just use the reverb on the GP-50. The Hall of Fame sounds a little better if you really pay close attention, but while playing, you can't really tell the difference.