Indexing and search tools require several key features in order to be considered a quality option for purchase. The PeerSpot community discussed some the aspects that they considered most important: the speed and frequency of indexing rated high on the list, as did customization of the tool's features (specifically overhead customization). Additionally the breadth and depth of indexing that it is capable of doing will tell a lot about an indexing/search tool. Other features mentioned include...
IBM Watson Discovery is an expensive product.
Cost-wise, it is very reasonable because it is cloud-based.