In the ER I work in we hire mostly EMT-B's as ER Techs. Out of the 5-6 ER Techs we have, 3 have EMT-B, 2 have their EMT-P, and 1 has an her LVN.
As for the job itself, from what I see day-to-day, the ER Techs spend most of their time doing the crap work that RN's don't want to deal. They push ER patients down to X-Ray/ CT, clean up after nasty patients, and resently I watched two of them take a homeless man into the tub room and clean him after he soiled himself. ( A rather fragrant patient too)
ER Tech can sometimes be a thankless job, but overall, all of our Techs seem happy and say they make more money as an ER Tech than the EMT-B's and EMT-P's do in our area. From my experience, ER Techs are some of the coolest people you can even meet, and they work their tails off. But again, that is how they are at my hospital so experiences may vary.