Golf Pad for iPhone is compatible with Apple Watch (all series). Pebble and Magellan Echo are supported in limited mode and can be discontinued at any time as the watches have been discontinued by the respective manufacturers.
There is no iPhone support for Samsung Gear/Galaxy watches and Android Wear at this time. iOS devices can sync with Samsung watches, however 'companion' apps are not supported. So one can download an app on the watch that runs completely independently and does not require a matching app on the phone. Golf Pad does rely on 'companion' app functionality: for example, a round has to be started or saved on the phone. This is true even when standalone mode is used during the round for rangefinder and shot tracking. When manufacturers add support for companion apps on iOS, we'll be happy to add Golf Pad watch app for iOS.