I bought this to carry a Yamaha MG-12 (which is the same size as the 12XU) to gigs, and have used it several times now.
The shaped foam inside keeps the mixer very firmly in place and there is a big space at the 'top' end of the mixer for carrying power cables, usw.
At a recent gig, a >=110kg band member stood on the closed and locked box (with the mixer inside!) and the box carried him with no issues. I think that's proof of how strong the construction is.
The hinges are of the 'lift-off' type so you can totally remove the lid by opening it about 180 degrees and then the lid lifts off the base. You can operate the mixer in the case base if you want to and there's plenty of space for air circulation (I don't do this) but there's no stay to stop the lid coming off, unless you rest it against a wall or something.
Would recommend this box as it's very solidly it's cheaper and better protection than buying the expensive optional Yamaha official rack-mount rails for the MG12 or MG12XU and using a shallow rack-mount case.
Having received my flight case, quickly and well packaged, I have to say, the quality of the item is fantastic. This particular case is a custom fit for my Yamaha MG12 XU and it is perfect. Excellent service and item.