Some good points were already brought up in the comments (IP5X, USB C charging), but I have the feeling that it's also just not a good fitness tracker/smartwatch.
I see a single unboxing of the watch from three weeks ago on Youtube and zero reviews on YT or websites. Just posts based on their PR release that it's available now. (Though some clearly already shipped.)
Thus, it's unfortunately very likely that the product is also not good at its main purpose, tracking activities, workouts and health. If it would only even come somewhat close to the performance of all the competitor smartwatches/trackers, they'd be louder about that part.
There are only about 400 units in existence, and they just started shipping June 30:
https://www.kickstarter.com/projects/unawatch/meet-una-the-m...
so it's been out for less than a month. That's why you've seen zero reviews on websites, it's an indie Kickstarter. They don't have the marketing budget of a big wearables brand.
It has a GPS, IMU, and heart rate sensor: That's enough, obviously, to track activities, workouts, and health which their competitors do with the exact same set of sensors. It remains to be seen how accurate those are, or how well the manufacturer and community can develop useful algorithms to turn raw sensor data into activity logs and actionable health insights, but step 1 is to release an MVP to get people wearing the watch and logging data, and step 2 is to use the data to improve the algorithms.