I have not noticed any additional measurements with Premium, only that some of them are evaluated and documented in more detail. The SPO2 measurement, for example, works just as well without Premium, but you are only shown 5 days instead of 30 and no "personal areas" are shown in the graphs. The oxygen content during sleep is also displayed with and without Premium.
Under the following link you have shown the various differences. It is mainly additional services like the "Coach" that you could benefit from if you want to.
https://www.pocket-lint.com/de-de...