For the price, these have good build quality. I got them from Amazon a couple years ago and they still look new. There's metal on the buds, the mic/button module, and both parts of the joint thing that connects/adjusts the length of the L/R wires.
These are directed towards people who want extra bass, and they fulfill that goal well for the price imo. I prefer the sound of the A151p v2 in this price range (under $50), but the build quality is nothing compared to the M-Duo and I don't like the hassle of having to wrap the wires around my ears every time. I agree with your recommendation, though. Only get this if you want extra bass.