I'm setting up a new home studio and I wanted to use my A&H Zed 18 (previously used in my live PA but redundant since the pandemic). I've bought the rack mounts for the mixer and with a little bit of tweaking, it's now sitting very firmly in this rack mount.
I read the previous comments about the problems with the nuts and frame both being powder coated, so I bought a cheap tap and thread set from screwfix and gently cut fresh threads in the existing holes. It didn't take much effort or strength and the screws fitted cleanly without any problems. I've not used the top bar, but the rack is very stable without it.
A couple of points to mention: I don't think this is going to be perfect for larger rack mount gear, the screw hole positioning is really aimed for maybe a maximum of 4U-6U pieces. I've only been able to use two holes on each side for the mixer, but that is still enough to get a good solid build.
The other thing to mention is that the plastic handle caps which fit over the bolts for the bottom cross bar were too weak to tighten the bolts, and came off, meaning I had to tighten them with a wrench. Nothing very serious, a mild nuisance and nothing more, but it would annoy me more if I didn't have my toolbox nearby.
I would buy these again, and I have actually ordered another couple for other studio gear.
I summary, these are perfectly usable with a little bit of care. I like how sturdy they are and the fact that they are slightly angled - it makes it easier to access and see the mixer, even if it's nearly at floor level. I've knocked off one star for overall and one for quality which I think is fair given the things I've mentioned. Still very happy.