It costs more, and they don’t last as long. Ceramics will lose effectiveness over time.Level 3 plates should cover .223/5.56, depending on load. Demolition Ranch tested some AR500 plates years ago by shooting something like 50 rounds of green-tip at a single plate and only like 2 rounds penetrated, IIRC. I think hotter, faster M193 might've taken less to get through. Most companies' 3+ designation means a special threat coverage i.e. M855, since 3+ isn't an NIJ rating.
However, I would advise not going with steel plates unless you really can't afford something better and need something right now. My first plates were AR500 Level 3 steel and they're damn near 10lbs a piece. Ungodly heavy. My current plates are Level 3+ ceramic/composite and weigh 4.9 lbs each. The difference means everything. I can wear the new ones 10 times longer than the steel plates, especially if I'm actively moving around the range or whatever. My friend Josh and I actually did the TRex Arms course-of-fire standards today in our plate carriers just to see how it affects stuff. After going through it twice each, the weight of the carriers+plates+gear was definitely taking their toll. So, if you can save your shoulders and back from an extra 10 lbs of unneeded weight, by all means do so. It just costs a little more. If all you can do is steel for now, then great. But don't let getting them stop you from saving up for an upgrade in the future.
Nope, not in Afghanistan. I work church security every week here in these crazy days in the USA. In this day and age, that's an important team to have in place. If it can be semi comfortably worn and comfortably concealed for 4 hours, then why not?And why do you think you need body armor? You aren't in Afghanistan. I served 3 tours in war zones in Southeast Asia and only wore body armor in one tour.