Right I got it today and had a mess about, I'm impressed its not perfect but the guitar sounds great through it with a few stomp boxes and then a marshall stack set up with a 57 on it.
There are a few down points:
There isnt much volume (don't know if its just my headphones)
Runs the battery down quick
When I upload a song into it to jam along with if I put distortion on my guitar it distorts the tracks aswell

But overall its worth the money and the free app.