I use this for hanging my Bb trumpet during practices in my flat where I am using a Silent Brass mute system and in-bell stands are a faff. It's a convenient motion to hang it below the stand (fixed to the stand upright) as I flip a page or rest, and I've also tried attaching it to the side of a flat-edge cabinet.
The end of the screw features a curved piece, so the clamp works best on round tube sections (like a music stand), but it did manage to grip a flat surface, too. It has a tendency to droop slightly from horizontal, but even with initial nervousness it never feels like it will fall off and damage the horn, and as long as it's placed gently the horn does not swing or knock against the stand. As with all K&M products I've found is extremely well-made and has reassuring weightiness and solidity; probably the only brand I'd trust not to drop my trumpet!