Checked my Poly hive and nucleus yesterday, they were full to bursting!
Considering that they were swarms, the full size poly hive went from 5 frames of eggs to 9 frames of brood and the 10th frame 50% drawn I was amazed. The nucleus went from no brood to 5 frames of brood and the 6th containing stores and all of that in the space of 10 days!
Super-ed the main hive and transferred the nucleus into a full size hive.
Compared to the swarms that I hived in wooden national brood boxes, which are doing well, the poly hive has almost double the brood.
I bought the 2 national hives to compare and so far I am more than convinced that they work better than wood.