The HM1900's style, fit, and function is much better than it's predecessor the HM1800. It feels more durable overall, fits better, and so far is easier to pair with a built-in audio voice letting you know set up features, pairing, and turning on. The 'hold down both volume buttons to turn off light' is a great feature to have as well.
This bluetooth's battery may not last as long as it's cousin's, but I will take a bet it will get near it's battery life for streaming music. It's cousin's, the HM1800, lasted me roughly 6 hours of constant music streaming. I will hazard a guess the HM1900 will outperform its listed battery length of 4.5 hours by at least a half hour. Who knows, might get 6+ hours out of it.