I have tried various amp modelling and multi-effects devices for years and never been satisfied. Although I own some wonderful vintage gear (Deluxe Reverb, Dual Showman Reverb), custom cabs, analog pedals, and they sound great, I wanted greater flexibility in performance. Purchasing a quality PA (QSC K12) I was prepared to save for a Kemper or Axe II rig. Then I saw the Mustang floor on videos for only about 7% of the cost of the rigs I was considering, I decided to try one.
Wow. It is absolutely performance grade kit.
It has by FAR the most intuitive interface I've seen on any such unit.
Key use notes:
1) Make certain to set the unit for the correct output target (e.g. combo, stack, PA). This is critical to your tone.
2) Use the amp controls as you would the real thing. I was not happy with the default "70s British" sound, so figuring it was a Plexi Marshall, I turned everything except "gain" and "presence" all the way up like Eric and Jimi, rolled back the tone on my guitar, and Voala! - woman tone.
3) If you are more old school, turn down the gain on the presets, I think too much gain obscures the character of the different amps (In the analog world too).
I am not saying this produces the most complex, rich, dynamic tones in the whole world, or is as flexible as more expensive units, but for most performance situations, you can easily get a wide variety of good, consistent, entertaining sounds that should satisfy your audience completely - with just this little critter plugged straight into the PA.
And - It does NOT have the tinny, scratchy, overtones I have heard in it's competitors.
For the price, it is the best music purchase I have ever made.