When given the go-ahead, Discover visits each site and prompts you for unspecified argument values. Performance Discover does its job quickly, and I experienced no lockups or crashes while using it. Many queries are answered as soon as the mouse is released. Others take just a few seconds to return. Retrieving the complete list of Looking Glass functions took less than 10 seconds.
Information is cached in memory to speed multiple retrievals.
There is no printed reference document for the browser or the viewer, although the online help is copious and organized. I am of mixed mind concerning the omission of a true reference document. This is a powerful product with features that can be combined in many interesting ways, and a comprehensive reference manual helps give me confidence that I am using product features to their fullest. Therefore, I think it's a shame that a general reference book wasn't included. I was impressed with Discover.