Sweet ! Just curious why do you want to hook up another item to the rig ? Is this so you can track them "live" ?
When I operate as net control for public service events, such as runs, bike races, etc., we usually have one runner in the pack with an APRS HT, and a tail vehicle behind the last contestant, also with an APRS beacon. If I'm operating with someone else they usually handle the APRS tracking on a laptop using an HT, but if I'm operating solo my laptop won't work with the software (64 bit laptops are a PITA - working on getting an older Toughbook from the county) so this will give me a low cost visual capability until either the county issues/gives me a Toughbook, or until I buy one myself and get it setup. Plus, visual indication of APRS beacons while driving on a separate GPS means I don't have to try and look through menus and screens on the FTM-350. The 350 is a nice rig, but I wish it didn't revert back to the main screen every time you transmit. With this, that won't be a problem.