It actually is what appealed to me in how it is presented. Can you give me an idea on how open it is? Do I need register an account to run it?

You can use the device as a fitness tracker without registering an account. And you can download activity files with a USB cable. But anything more, including the satellite connectivity, requires registering an account.

I am not sure what you can do without an account, because I created an account on day 1.

It connects to the phone over Bluetooth. Many operations need your phone to have internet. There is a kind of primitive app platform. The only app I really use is for Home Assistant, it makes https requests to HA over the phone. I connected it to Strava too, it can realtime send heart rate to that app without going to the internet, but it required jumping a few hoops in settings.