I love to use props whenever I play, and one of my favorite monsters to drop on my players is a mimic. They are fun and always a surprise, however you have to be careful of how you do it.
My personal opinion is to get them used to seeing elements within your dungeons. Props like chests, barrels, bookcases and so on. Once they get used to these figures, why not have one of the barrels actually be a mimic in the same style!
Feel free to use this free mimic design for your tables. For this patreon supported post I am offering the free Front and Back of the mimic barrel, and two separate barrel designs.