There are so many drawbacks with poly, the market is muddled with many designs and most are incompatible with anything else due to dimensions or design flaws. Abelo seem to have sorted out a poly hive that at least can be used with any wooden kit but has its own problems.Yeah.....I looked at the poly stuff....but is that environmentally friendly?
Note, these comments are about National kit. If you were to go Langstroth, you have the burden of obtaining bees on an unpopular frame size and you will be restricted in your choice of supplier or face another faff of converting frames while you get them established.
I started with cedar nationals, tried various poly options and I've replaced the lot with cedar. Colonies in cedar did equally well.
Double brood standard national deeps are so flexible as the cavity can be reduced to whatever size your colony requires with some packer dummy boards and these can be removed for extra space if/when required. It certainly doesn't mean you have twice the number of frames to inspect, anyone lifting off top boxes and lifting every frame needs to ask himself why? It's not necessary.
I've over Wintered in double format for years, usually eight or nine frames per box, the bees love the set up.
I'd take advantage of the Maisemore sale ( I have ) and go for cedar nationals ( if I've left any )