A quality hinged closure will not open on its own: tension-based and box-latch hinge mechanisms require deliberate pressure to release, which means the piece stays put through the movements of daily wear.
Visually Speaking
The box clasp is the standard closure for pearl necklaces and multi-strand bracelets. Its flat profile keeps the closure visually consistent with the strand's drape, a design requirement that rounder or heavier mechanisms can't meet as easily.
A Notable Quality
The sound metal bangles produce when they contact each other during movement is not an issue in several traditions. In fact, it is an actively valued, recognized sensory dimension of the bangle-wearing experience that has been part of the form's appeal for centuries.