If you've got an RFguys Prorib, and are using it on a regular serial port, you're probably not going to notice any issues. If, on the other hand, you're using it with a USB serial adapter, you might wish to solder a jumper from pin 5 to the metal shield on the DB-9 connector.
The Prorib doesn't have a manual on/off switch - it relies entirely upon it's auto-on circuit for that. Without a good ground, the auto-on doesn't work. And the ground pin - pin 5 - doesn't always provide a reliable ground, depending on the USB serial adapter. On the other hand, the connector shield DOES provide a good ground, so running a jumper will allow the Prorib to work properly.
Or you could buy one of the various Motorola RIB knockoffs that cost $20-$30 depending on circumstances and seller.