I'm using Paynes poly nationals that come with a flimsey 1mm top cover - bee killers because no top bee space (for me anyway)
I was never happy with them, no matter how you try and clear the bees with smoke or a brush and even gently sliding the sheet into place there were bees trapped, so to fix it I made clear crown boards with 8mm BS and put a 30mm feed hole in the centre fitted with a removable clear plug. The result is no bees crushed, in fact it completely changes beekeeping for me, inspections, feeding and a quick look on a warm winters day without opening are now possible, and I don't have to hoosh all the bees off the tops of the frames and agitating them.
I'm working on a similar one for nucs now as attached!
Definitely worth considering for the small amount of money involved.