What should I consider in choosing a built in sharpener or a separate one?

The choice is basically depending on the habits of each market, i.e. how a slicer is used traditionally.

We can say that the separate sharpener makes the washing process faster, because the blade is fully covered therefore the operation is quicker.

On the other hand, with the built in sharpener, as it is always positioned already on the slicer, there is no risk of loss and misplacement.