Limited information about returned results. Ranking of results cannot be modified and seems random. Seems to be case sensitive. It can do a content, natural language query and opens the PDF to the exact page of the hit. The hit words are highlighted.
Biggest problem is it only searches PDFs.
It is hard for people to understand a natural language query when they are used to simple word matching. Ease of set up. This site does not combine an index that includes my 4 different URL's. It is a temporary solution, much functionality is needed and when sote load and content increase it will not work. It doesn't work very well at all.