Hi,
Smart search results web part has a pager assigned to it by default which is of type
DataPager so there is no need to add
Unipager to set the pager and its size. You can configure it in your
Smart search results ->Page size property.
More details about these two controls can be found in documentation -
UniPager,
DataPager.
I hope this answer will make paging options clearer for you.
Best regards,
Filip Ligac