The Poké Ball Plus is perhaps more useful for Pokémon Go users, presuming they can get it to work properly.
Pairing the Poké Ball Plus with your smartphone may take some trial and error. With Bluetooth enabled, enter the main menu on Pokémon Go. From there, go into the Settings menu. You’ll see an option for Poké Ball Plus.
With your Poké Ball Plus in hand, click in the button on top of the accessory. This will allow your phone to find it. Then click the Poké Ball Plus option to initiate a pop-up that will ask to enable the Poké Ball Plus. The Poké Ball Plus icon on the main gameplay overworld will then illuminate to confirm that the game and device are paired.

Poké Ball Plus icon in Pokémon Go
That Poké Ball in the upper right-hand corner will light up when the device is connected.
 Niantic/The Pokémon Company via Polygon

You may require additional troubleshooting, especially if your accessory is constantly disconnecting from the game (which was our experience). This is what the Pokémon Go support site recommends:
On iOS devices:
Open the Settings app and tap Bluetooth.
Tap the Bluetooth toggle to turn Bluetooth on.
Press the top button on the Poké Ball Plus to make the accessory discoverable.
Tap Pokémon PBP (Poké Ball Plus) on the My Devices or Other Devices list.
Open the Pokémon GO app.
On the main screen, tap the Poké Ball icon at the bottom to open the Main Menu.
At the top right, tap Settings.
Tap Poké Ball Plus.
Press the top button on the Poké Ball Plus to make the accessory discoverable.
Tap your Poké Ball Plus on the Available Devices. It will vibrate when connected.
On Android devices (instructions may differ depending on device):
Open your device’s Settings menu.
Tap the Bluetooth toggle to turn Bluetooth on.
Tap Search for devices, or Refresh to scan for nearby devices.
Press the top button on the Poké Ball Plus to make the accessory discoverable.
Tap Pokémon PBP (Poké Ball Plus) on the list of available devices.
Open the Pokémon GO app.
On the main screen, tap the Poké Ball icon at the bottom to open the Main Menu.
At the top right, tap Settings.
Tap Poké Ball Plus.
Press the top button on the Poké Ball Plus to make the accessory discoverable.
Tap your Poké Ball Plus on the Available Devices list. It will vibrate when connected.
From there, you can start catching Pokémon and collecting items.