Excellent sound, but it doesn't handle third-party operdrive pedals well.
The plugin itself has an excellent sound; it has everything you'd expect from a vintage Marshall. It includes a booster that helps with the more saturated tones and handles third-party IRs very well.
The only weakness I find is that when you add overdrive or distortion pedals, or plugins from other brands, to it, the sound becomes muddy and dull. The built-in booster works well, but if you want to add another layer of color to the sound, it doesn't handle it very well. That's just my personal opinion.