The enhancement of Special:Search by providing an advanced parameters form and improving how namespaces for a search query are selected seems quite helpful.
My wiki's run on shared hosting plans so using using Extension:CirrusSearch (Elasticsearch) is not possible.
During my initial testing without having Extension:CirrusSearch installed everything still seems to work as expected. So I am left to ask what functionality requires having Extension:CirrusSearch and whether or not this can be installed on wiki's without Extension:CirrusSearch.