I worked Security full-time for about 5 years. Prime job was S/O-EMT, but after enough time, was a dispatcher, FTO, Armed S/O, and a bit of everything else. (Other Duties As Assigned was 95% of my job). Part of that was that I had been there for so long (Averaged a little short of 100% turnover yearly), and part of that was that I was intelligent and enjoyed the work.
When I worked as an S/O-EMT, my job was essentially, be a Security Officer. Then jump in a telephone booth and come out as Super EMT in the event of a medical emergency. Otherwise you're just another S/O (except in our case, you're the only S/O that can abandon a post... because you drop everything for a Medical call). And you'll be doing 95%-99% Security work. Luckily in PA, there is no training requirment UNLESS you are armed (or carrying a baton), so there is no "cost" to get into it. My advice is to go in with an open mind. For every S/O-EMT we had that enjoyed it, we had half a dozen that burned out and bailed because it wasn't traditional EMS.
I still work armed details occasionally (VERY occasionally). I have BLS gear with me in those cases, and while I don't get paid "more" because I'm an EMT, I think I get more "fun" assignments because I am. In those cases, I'm Security first, last, and always. Only if I have adequate backup and the situation allows it can I play "medic" - Sometimes that happens, sometimes it doesn't.
In the latter bit - one of the hardest things for me as a medic was to hold a position 15' from someone that got slashed across the chest. I had NO backup (they were chasing the do-er). His buddies eventually threw him in a car and drove to the hospital.