The coolest part to me is that they're using the S5 watch SoC to power it. Pretty cool that Apple's various hardware teams can just grab a part off the shelf to use in a completely different class of device. I'd love to see them reintroduce AirPort routers powered by an A-series chip.
In the meantime, they're super convenient for having my Time Capsule back up my Mac, and for piping audio via an Airport Express to the speakers I use with my projector setup.