My bees just didn’t seem to get on with plastic foundation; very slow to draw it out and would rather expand upwards than sideways.
I’ve since binned all the plastic and gone for wax foundation. Bees seem much happier, expanding quicker etc.
A split I made back on 5th July has just reached the stage of being quite strong and filling the nuc. Back in the summer I wouldn’t have hesitated to put it into a hive but with the brood nest now shrinking, I think they’d over-winter better in a full poly nuc than an empty wooden hive.