I've been looking at this in recent weeks too. In the end I went for these poly mating hives:
Mating Hive for Queen Rearing - Beekeeping Supplies UK
Price is a little bit cheaper at around £10, but arguably less durable. I chose these in the end because they came with a clear bit of plastic as a CB, whereas I couldn't seem to find anything about the rainbow hives that mentioned any sort of CB. I can never resist just being able to lift the lid peek in the top and see what's going on or if there are any issues. Although I've played around with these mating hives, and got them set up with strips of foundation etc. they haven't been fully deployed with any bees yet (plan is to do that tomorrow), so I can't really comment on using them in practice. Only thing I will say is that it's difficult sliding the front up and down to open close the entrance at first, but once you've done it a few times it eases up.
To be honest the insulative value wasn't much of an issue as far as I was concerned. I only plan to use them for a few weeks in the summer - just long enough for a queen to get mated and go through a whole brood cycle before moving the queen on.
The only thing I thought might be an issue was comb being built in the feeder as it empties out, but we'll see.
I only keep 2/3 hives at a time, and although I wanted to try out queen rearing it was important to me that it didn't adversely affect my production colonies, so through using the Ben Harden method, and mini mating hives that only need a cupful of bees my main hives should be able to just get on with all that honey production with only minimal disturbance. We'll see how that works in practice!