Both have sound vibration speeds of up to 62000 /min. Therefore, the 4300 model is sufficient.
I would not go below 4300 (e.g. 3100), these models only have sound vibration speeds of up to 31000 /min.

This sonic brush was recommended to me by my dental hygienist because it is completely sufficient.
Top price-performance ratio!
I am very satisfied. It is more difficult to find your personal brush attachments. I had to buy several (expensive). Tip: There are also two packs of attachments.