More useful for track rats using iPhone & Harry's Lap Timer but still works with other GPS based applications (i.e. navigation), external antenna attachment for the iPad and iPhone. iPhone internal GPS operates at 1hz, this is the only Apple-approved device that provides real 5Hz update rate for iOS apps.
Amazon and manufacturer are the only places that sells these. I paid $105 shipped, will sell for $85 shipped to anywhere in 48 states. Does not come with original box/instructions but includes charging usb cable. All documentation can be downloaded here:
Check my iTrader feedback. PM if interested.