1.) When do you / would you carry it?
2.) What are your experiences with it?
There are two serious questions that need to be considered. The first you answered - the threat level you expect to face - as a common handgun, probably nothing exotic. That's a good thing in relative terms. A level II vest should do well but a Level IIIA would be better.
The second question is harder to answer. And that question is -- what kind of capabilities do your attackers have? Are they solo actors in jail? Are they part of a gang? Is your testimony a crucial factor for their conviction? Is it likely you could get whacked purely from a revenge perspective?
In other words, how much "worth" do you have as a target of assassination? If it's a personal revenge thing or you are a high value target, consider that body armor should be a constant for a while.
If the arrestee is a gang member and has "friends" who can observe you and plan their attack, body armor AND a weapon should always be worn.
If we're talking a lone actor who's in jail, then his friends or cohorts may try something as a "favor", but amatuers have a way of being spotted thru clumsy work.
Start, of course, by being
predictably unpredictable. Go to work early some days, late other days, but never the same day of the week. Take different routes to the office or home. Take different trains or busses. Deprive them the ability to predict your movements. Of course your "weak points" are your home, office and local courts (you are a lawyer, right?). Be extra vigilant around these areas.
Plan on wearing the vest all day long since the focal points for an attack will be at/near these points. Wearing concealable armor avoids alerting the shooter that he should be taking head shots.