I have been testing #Lysons
3 frame poly Langstroth Nucs as Mating Nucs this year and will be expanding on their use next season as they have increased the number and quality of Mated Queens this year and allow you to leave the queen in there longer to develop a good laying pattern.
You can buy a separate top feeder for them that works a treat. costs around £7.50
They also over winter well so they are good as a dual use to build up to a larger Nuc/Hive or have a ready to go mating nuc and an over winter Queen ready to go.
The only problem is with this hive it impossible to use sugar blocks or fondant on these hive for overwintering.
So a solution is to make and Eke the easiest way i have found is to buy a second feeder and cut the bottom out of it. I used an old bread knife and a blow torch. Heat up the knife and trim out the bottom. Do this outside there will be some nasty fumes from the polystyrene. The Feeder now Eke is still rigid and just as solid with no bottom.