Yup, armbands are NOT transporters, they are personal signal enhancers. We have seen other types of enhancers also, like the cylinders Barclay used in 'Ship in a bottle' .
I hated the mini self-contained transporter used in Nemisis, it was just to much of a Magical tech devices.
I try to rationalize the wearable transporter has having a dedicated, self-contained transporter on the ship somewhere. Otherwise it's ridiculous and stupid. Transporters are huge devices that take up two decks and would requite utterly ENORMOUS levels of power to operate. Even stupider with the device in NEM is that it could transport itself!
How the fuck does that work?!
The armbands we see in the series are simply there to give a stronger, sure-thing, signal lock. They're not self-contained transporters. They're wearable versions of those three polls we'd see them set-up from time to time.
The pin in NEM? Dedicated transporter on the ship that's not otherwise accessible. (But probably could with time to get to it, time the crew didn't have.)