> We filtered out PISA Search and Manticore because neither of them offers search-as-you-type and facet search features

Manticore does support facet search and it's quite powerful in Manticore:

- docs - https://manual.manticoresearch.com/Searching/Faceted_search#...

- interactive course - https://play.manticoresearch.com/faceting/

Search-as-you-type depends more on the client, not on the backend. However, Manticore provides the autocomplete and fuzzy features (both in beta stage though). More info here https://github.com/manticoresoftware/manticoresearch/issues/...

The "drawback": PostgreSQL database synchronization.