My OPINION, personal transponder...less money ($80) and with more racers going DSM, getting an open freq was no problem racing yesterday (running JR XS3). But this really wasn't a question about the track....

edit...

You can retune to another freq with synth radio if needed. You're screwed if your track loaner transponder isn't in the rack when it's time to race because the last guy didn't put it back and now he's out there marshalling.