If it ends up compatible with project fi, their extra data-only device comes free (at $10/GB like the rest of the plan). Might make this the first smart watch I've found appealing.
The problem with that is that it would have to be completely decoupled from your phone since Project Fi only supports the Pixel and Apple Watch only supports iOS.
If you don't want the watch to interact with your phone at all, then you would be fine. But you'd presumably be losing quite a bit of functionality by doing so.