Maybe we can get some comments from people that use FlightAlert XT from CompuSense. We read about it via a press release from XChange:

FlightAlert XT combines on-the-fly error checking of QuarkXPress documents with one of the most powerful Collect For Output engines available.

FlightAlert scans QuarkXPress documents for the key problems that regularly waste time, money and film. It is unique among the error-checking products in that there is no need to invoke or apply FlightAlert. It operates in the background as users work making it an ideal solution for integration into busy production and prepress workflows.

FlightAlert can be set to scan on Open, Close, Save, Save As, Save Page as EPS and Collect for Output. By concentrating on the core of common problems, each FlightAlert scan is virtually instantaneous on small documents and takes a negligible amount of time even on large documents.
Source: http://members.whattheythink.com/news/newslink.cfm?id=37503

Who has used both FlightCheck (the original and patented) and FlightAlert. What features do you think are better in one than the other? How is the price value better or worse?