Compared to similar dynamic scripting languages, Q is very vast. Compared to statically compiled languages, it can be surprisingly competitive, but is usually slower. The truly distinctive thing about Q is its efficiency as a user interface: at a REPL you can rattle off a short sequence of characters to transform and interrogate large datasets at interactive speeds and flexibly debug complex distributed systems live. In the right hands, it's a stunningly effective rapid-application-development tool (the above "quant desk scenario"); this was perhaps even more true in the k2 days when it was possible to build ugly but blisteringly fast and utilitarian data-bound GUIs for K programs in a few lines of code. There's certainly an abundance of romanticism and mythology surrounding it, but some of the claims are real and enduringly unmatched.