We used Blueberries as our main nappies for nursery (poppered ones) and they had no problems at all. When I had to work more hours I sent her in fitteds and wool as that was what we used at home, and they had no problems with that either, I just made sure it was one or the other each day (ie all fitteds or all pockets) rather than swapping systems iyswim.
If I needed to stretch my stash and use an odd nappy I would put it on in the morning, as then they just had to figure out how to undo it. We never had any problems.
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