I also use the mann lake one. And Im happy with it. Ive only kept bees in it for a little over a week though. I just move the frame from topside to down below every night, opened the door,and put a nuc lid on top. One thing was because the thing was going out in the afternoon I put wet sponges in for water. and if your closing it up after the sun comes up you loose a little field force.
Also have this one, and like it. I wish I could adjust the glass closer to the frame, the bees will go double deep on it (bees on the comb, bees on the glass) and makes it hard to see. Best would be if I could adjust the glass out for frame installation and then back in toward the frame for observation. I don't have time to mess with it though. What I do have time to mess with, and the thing is on my workbench, is to put a "piezo undersaddle" guitar pickup underneath the ears of the frames, run the wires out to a pre-amp and headphone amplifier, and let the kids listen in to the communication on the combs. I also have a pluggable web-cam that I want to install on an arm to look at the observation frame and run that out to a larger screen. I've got the parts for that, but what I really need is some anti-glare coating on the glass. Camera only shows reflections of everything else.
I don't know what it does for sales, but people really do like it. If I was going to keep the colony installed for several weeks, I would remove the QX from under the observation frame so she could keep a viable colony going.