Instead of requiring another app to control Keynote presentations from another device, Apple updated Keynote on iOS to act as a remote.
In order to get the remote functionality to work, there's some extra steps you'll need to take both on your iOS device, and your Mac.
Before you can control a presentation on another device (Mac or iOS), you'll need to enable remote control. To enable it on a Mac, launch Keynote and click on File > Preferences. From there, select the Remotes section and check the box to enable the feature.
On iOS, you'll need to launch a presentation and then tap on the settings icon (the wrench) and select Presentation Tools > Allow Remote Control; toggle the switch to the on position.
After enabling the ability to use a remote control with Keynote, you will need to connect the two devices to one another. For iOS devices either a shared Wi-Fi network or Bluetooth connection is required. To control a presentation on a Mac from an iOS device, only a shared Wi-Fi network will work.
In order to use one iOS device to control Keynote on another iOS device, tap on the remote icon on the main screen in Keynote on the device you want to act as a remote. Follow the prompts to make the device available (indicated by an animated blue dot in the middle of your screen). On the device you want to have the slideshow displayed on, launch the slideshow and navigate to the same settings screen where you previously enabled remotes. There you will see the remote device listed (pictured above). Tap on Link and verify the same security code is displayed on both devices.
To use an iOS device as a remote for a presentation on a Mac, launch the iOS app and tap on the remote icon. Again, follow the prompts until the blue dot is animated, indicating your device is available. On the Mac navigate back to Remotes settings in preferences and click on "Link" located next to the device you'd like to use as a remote (pictured above). Confirm the security code.
Once devices are linked, launch the presentation and on the remote device, tap the remote icon followed by the big green play button.
By swiping through your slides on the remote, the slides will advance on your presentation. There are a few different ways to arrange slides on the remote, so play around with the settings and find the one that works best for you.