When it gets colder while walking, I'd add an extra fleece as a mid layer and when we stop to eat, I would put it on too, or I'd wear a down jacket if it's dry.
However when it's wet, it seems like taking off outer shell to add mid layer is troublesome. Isn't it better to get a synthetic down jacket that can be worn on top of my shell, even if it's a bit wet? This way I can just throw it on top. I've heard this can be referred to as belay jacket.
What are the pros and cons? What have been your experiences in, e.g. Scottish weather?
PS. My shell is actually Paramo, which in my experience will be more breathable than a membrane, so I don't believe I'd be getting wet from the inside.