The new Pokémon Go Plus finally went on sale 16 September and is apparently already sold out on Amazon. Is it worth shelling out money for this? If you want to hatch your eggs faster, perhaps.
The Pokémon Go Plus finally becomes the pedometer the original Pokémon Go app should have been. With your phone locked and in your pocket, the Pokémon Go Plus will track the distance walked without your needing to keep the Pokémon Go app actively on with your phone screen unlocked.
It will either function as a wearable attached to a bracelet or you can clip it onto a belt or other wearable.
Still, you will need to have the device connected to your phone via Bluetooth, which will sap some battery but not as much as keeping Pokémon Go on all the time. This will of course help keep your eyes in front of you instead of on your phone - definitely a safer way of playing Pokémon Go.
It's also good as a notifier of nearby Pokémon: the device will flash green for a known Pokémon and yellow for a Pokémon you haven't caught before. You can then choose to either whip out your phone to catch it or press the button on the Pokémon Go Plus device to catch it from there.
Players have reported that there's a lower catch rate if you use the device, as it doesn't let you choose things like Berries or higher-level Pokéballs. So if it's an unknown Pokémon you'd be better off catching it manually.