Personal anecdote: I had three Jawbone fitness trackers that stopped working within months. Granted, two of them were replaced by Jawbone, but after a third I stopped bothering. The bracelet design was thin and elegant as opposed to the bulky Fitbits. Inside, jawbone bracelets had several very small PCBs arranged in a row, connected by wires, with a protection layer of epoxy glue or something. The whole construction was flexible but - I imagine - pretty prone to wear and tear. Whereas Fitbit went for hard casing design that was inserted into the rubber strap. To me it is a story of finding the right balance between aesthetics, reliability, and functionality