How realistic are the various apps at simulating, say, a 1200-ranked human player?

I'd love at app that really plays at my skill level, but my experience with older software was that the computer "dumbed itself down" simply by playing completely silly moves at times. (Of course, I played silly moves as well, so maybe it was accurate... But it didn't feel that way.)

Stockfish can play a pretty convincing ~1200-1400uscf game. (At least for that rating range 30 years ago.) It won't start making egregiously dumb moves until it's in the "If I were a person I'd resign, but I'm a computer so here take all of my material before you checkmate me" phase, though many of its opening choices are obviously third- or fourth-best.