Began my first year with old galv bendy QXs (inherited from the deceased allotment beekeeper) and saw that bees propolised & braced them to hell; as a consequence the uneven QX never went back flush, and getting bees to shift when putting it back on was like herding cats on a dark night. Green plastic flat QXs are no different, just a modern version of the same but without the sharp metal slot edges that wear out bee wings.
Waste of time, irritates bees, irritates me, demonstrates that the equipment is inefficient.
Well, I used them for a few months when they became popular (about fifteen years ago?) at about the same time Thorne put out the news that in one production run the slots were inaccurate.
Setting that aside, it is self-evident to me to that to put two flat surfaces together (alright, top bars have gaps) with ridges of propolis, brace comb and moving bees in-between is going to end in tears, if not when the bees are smoked to get the QX on, then when the box goes on and compresses the QX.
Yes, I use the same cheap method because it works well, but by the same token will pay for an expensive wood-framed QX because that also works most efficiently.
The QX frame sets the gap at one beespace. Brace comb will only appear if the beekeeper is late with adding box space, by which time they'll just as likely to have braced side bars and crownboard.
Always do, JBM, every day, but in this case I don't intend to use a piece of equipment made cheaply but badly by manufacturers that put price before effective product about 90 years ago.