I agree on wearing shelled insulation on the move. It would be too warm in most cases.
Example of using my windshirt and fleece mid layer combination in practice on the trail with a light base layer tee:
* Windshirt with base layer with cold wind or light/sporadic precip
* Windshirt and base layer when topping out on an exposed ridge or downhill walking when exertion has lowered and it is too cool for the base layer alone.
*Fleece mid layer with base layer for additional warmth with good moisture transfer and breathability. As above with situations with less exertion, like level and downhill walking.
*Windshirt and fleece together for rest stops and camp.
*Fleece plus rain gear for wet rest stops and cold precip or precip with lower exertion, as with the windshirt. Wet rest stops will often find me damp from exertion with rain gear. Adding a fleece layer will allow me to continue to dry out without getting chilled (hypothermic) where a thin shelled insulated item just traps the moisture and may get my main insulation item wet as well.
*Windshirt, fleece and rain gear all together for colder rest stop or camp.
*Fleece for sleep to extend the range of my sleeping bag or quilt.
*Wearing the fleece mid layer alone while my base lyer dries from washing or wet with perspiration.
The real crux of my argument concerns how a thin insulated item fits into a coordinated UL clothing system, particularly where a windshirt is included. With the windshirt, you are already halfway there. Adding yet another pair of shells and some light fill doesn't make sense to me, especially when those shells don't breathe well and the combination isn't all that warm. The Nano Puff ends up being a single purpose item that is only useful in a limited temperature range at rest.
The argument is very similar to the issues with soft shell jackets: additional weight with limited protection from cold or rain. If you have a windshirt, an insulation layer and a rain shell, there's little need for a soft shell.