I’ve used polyhives over the last 18 months mainly for my out-apiaries as lighter. Generally I like them, as so light and bees over winter well.
I have a large plastic tub that I put a bleach solution in (or washing soda) if a brood box needs cleaning due to swopping between colonies. I dunk each side in it for 20 mins or more and hold down with a couple of house bricks. Works a treat.
I use the Paradise (Finnish) boxes available from Bee Equipment or Modern Beekeeping. They only hold 10 frames but most of my colonies need 16 frames so would need double brood anyway.
Only thing I don’t like, is the runners are flat and bottom bee space doesn’t allow space for an elevated runner, so compared to wooden boxes with runners that leave a bee space below the frame you have to be very careful when lifting and replacing frames, not to crush bees by moving them out the way. Find this slows down inspections. If I was buying again I would choose a polyhive that has a better runner system. Interested to hear from anyone else using these types of boxes if they have any tips in this area?