I am using QE's on some hives this year for the first time and am really liking the results so far. I'd avoided them due to so much criticism/controversy before. A local mentor showed me his method and it has worked great. I find I don't have to disturb the broodnest for honey-related reasons nearly as much as when I did not use them. I'm trying out a QE over three 8-frame mediums used for broodnest, plus top entrances over the QE. So far this has worked really well and I'll post here for other newer beeks to consider.
What seems to really matter is *not* putting the QE on till the hive is nicely booming, then pulling some frames from below that are part-filled with nectar (I use all mediums) to bait the new box I'm placing above the excluder and alternate those nectar-frames with foundation if I don't have drawn comb. I replace what I took from below with foundation. All of this only once the flow is going and the bees need more room too. I'm getting a LOT more comb drawn out this year this way, which I need and ironically, better honey production than I've had in the past, probably due to the easier management.
Since my apiary has expanded a lot last year and this spring, I'm short on drawn comb so it's been easy with the QE on to pull frames of capped honey, go extract them and pop them right back on for the bees to work again. All without disturbing anyone below the QE. This has been GREAT.
My mentor uses another trick I may try- with a flat excluder (no wood on edges) he turns it sideways so that it does not cover the bee space between the two outermost frames and the box sides. It seems to give them another easy path to stash honey and since the queen is less likely to be traveling on the outermost frames, still works in most cases to keep her in her realm.
Anyway, using the QEs has been totally different than I imagined it to be from reading about it. Especially after my mentor pointed out the most critical parts: not putting them on without a good flow, top entrances, and something to lure them to learn to cross it.