Pro Mesh network allows for further ranges
HomeKit connects via bluetooth inside the home (to reach out of the home they require an Apple TV), and each connected device will pass along the information to the next device. This creates a 'mesh' network, where all the points relay the message along. This helps to extend the range of the network further than what would be possible if the hub connected to each device individually.
Pro Fully supports Apple's HomeKit
HomeKit is Apple's smart home ecosystem and is tightly integrated with Siri. It provides scenes, which you can describe as groups of actions that all take effect with a single command. For example (once configured), sauing "Hey Siri, Goodnight" could turn all your connected lights off, lock your doors, turn your thermostat down a few degrees, and turn on your connected security camera.
Con Limited to Insteon and HomeKit devices
While there are doezens of other standards available (WeMo, Nest, and SmartThings to name some of the bigger ones), the Insteon Hub Pro only works with their own devices as well as devices which are HomeKit compatible. This reduces your choice when it comes to buying new smart home products, where other hubs support multiple ecosystems allowing for the best selection of smart home gadgets.