I'm pretty sure the GPS signal only works if there is a data connection present. I've got this card, but I'm being sent the Compass 597 today, and should be here in a few hours.
I'm also pretty sure it updates only every 5 minutes, but I've not really messed with that part much. There is a label that says MPH, so, I would assume it updates more frequently. I had a hard time getting IG to recognize the port and receive any of the NMEA data though, so I stopped messing with it and just use my BU-353 for now.