I have no idea why people adopted brass in the A/V business. It's known for being pretty, heavy, and weak. Everything should either be steel (when you care about absolute strength) or aluminum (when you care about strength/weight ratio). I often think that the companies that set the standards for machining in A/V don't know much about machining ("hey let's have people attach all the parts that aren't supposed to twist using threads and baby pins").
Nice find by the way--can't have too many adapters. I carry a big ziplock of Manfrotto adapters of every flavor when I open-tape. The last time I bought off-brand, I had to take them to the machine shop and run threadsavers over all of the threads. I wonder if the other Neewer adapter types are good too.
FWIW, B H photo sells the manfrotto adapters (actually everything manfrotto) with a significant education discount (if you can get a university email address).