The Cor is the next generation on from the Arc which has a monochrome OLED display while the Cor is now colour. It has the usual complement of measurements, steps, sleep tracking, calories (made up as it's not tracking anything you eat etc) and pulse rate via n optical sensor under the body of the unit.
It's also possible to get notification from various apps and these can be enabled and disabled in the Mi Fit app.
Though the display is colour, it doesn't really add much to the previous and unless a preset display is chosen, some displays can affect battery life (as they get updated more often).
Step counting, heart rate and sleep tracking are comparable with the Fitbit AltaHR (wouldn't surprise if the actual electronics internally were the same or very similar), where Amazfit does excel is in price, the Cor can be had for around $40 from your favourite Chinese site. It's also waterproof to 5ATM so can be used for swimming and snorkelling and other water sports without fear of damaging it.
Amazfit are definitely a brand to watch in the fitness tracking department and they're constantly coming out with new products.
Recommended in terms of price and functionality, though the Mi Fit app doesn't yet compete with say Fitbit's, also battery life is claimed at 20 days and though it might not actually quite reach that, it will definitely last a week or 2 on a single 2.5hr charge.
