So I needed a harmonica holder which I could use on a stage performance and this seemed like the best option for a reasonable price.
The clamp works great! I've had no problems with it.
The adjustment screws do their job well enough but it's clearly the part with the highest failure risk. They have a tendency to unscrew themselves after many uses but it's very simple to retighten them and as long as you check them at regular intervals I see no risk of it failing on stage. Just to be clear, they don't become loose they just unscrew themselves because of the process of tightening them and retightening them, they hold just as well but if left unchecked the screws may come out completely which would be a pain.
It's worth noting that the bar which goes around your neck is in the wrong orientation in the picture (not Thomanns fault really as the manufacturer has the same picture). The small indent in the rubber (don't actually know if it's rubber but the soft material) should be at the back and correspond to where the back of the harmonica sits.
Overall great product for the price!