https://shavercheck.com/braun-series9-original-vs-updated/#Why-was-the-Series-9-updated-twice
Performance — are the newer Series 9 versions better?
Strictly from a performance standpoint most likely no, there isn’t a significant difference between the various Series 9 generations in this regard.
If you already bought the original Series 9 you can also use the new shaving heads (92s, 92b, 92M) used by the newer shavers and I actually recommend you to do so.
They are backward compatible and will fit the 90xx models perfectly.
As for the current widely available Series 9 models, the 92xx and 93xx, I’ve actually tested them side by side and I can honestly say that there’s really no performance difference between them.