Yes, I like to keep it on all the time, or at least control when it switches off instead of having to babysit the button. I'm not too worried about fresh air, as I noticed the 2017 model is leaky in general compared to e.g. a new Edge or the Explorer I had before. You still smell some car fumes (diesel, so not my own) even when in re-circulation. But It is usually just for those stretches of highway, and when I leave the main roads I leave fresh forest air in anyway.
Since they allow it on non-windscreen modes, I'm just puzzled they don't on that windscreen+ feet mode.
Other car brands allow this, but not Ford it seems, so I was hoping for a secret ForScan setting.