This foot switch is a genial thing if we are speaking about fast and comfy amp mode switching. I have Marshall MG30GFX and this pedal works perfectly with this amp.
About pros: its intuitive and easy to use and will serve you perfectly. Allows to program your Marshall amp, so you could switch amp modes with your foot the same time you are playing, without stopping playing.
About cons: in the beginning its a little bit hard to understand how to program this pedal, but when u set up everything (all presets), it will do what it has to do perfectly.
Couclusion:
It does what it should do and you need that if you want to maximise your Marshall amp features