The key differences are that no centralised "Web2" platform (e.g. Google, Apple) will see, own or sell your raw data - only you can do all these things.
The second key difference is data from multiple devices can be streamed all to your personal data wallet, allowing algorithms to analyse this data holistically.
Algorithms are also no longer proprietary - meaning anyone (students, entrepreneurs, communities, start-ups) can develop solutions for your wearables. This means as a user, you can shop around for different solutions meaning you are no longer tied to using the software of your chosen hardware provider.
No, you will own your biometric data. The raw data will only be able to be read and accessed by you. However, the big data metrics (which may contain your data) will be visible to those who are permissioned to analyse your data. This analysis will be scrubbed of all personal identifying metrics such as name, location, age, IP address, cookie identifiers etc.