The build quality is ok. A few of the connections have been unhappy and Thomann replaced the units free of charge, but the connectors to the headphone jacks are generally all a bit moveable.
They are really fine for stage use overall, just don't over feed them with signal as they have a limiter built in, and we find that some people want to more volume that the unit can provide to in ears. They don't go very low on the impedance at all, but if you are looking for a budget solution for ear buds then this will work for you. Overall they have served us well for what we bought them for, which was stage in ears in a house of worship. And they are balanced, which is really great and at that price point, they seem to be pretty good. I'd buy them again.