I would flush mount a regular speaker as this should give you much more controlled audio. This is a common practice in many environments as it gets the speakers out of the main room and gives a similar effect to in-wall, but typically with better sound at a lower price point.
For in-walls, you would really want something that you could get a back box for, which ends up costing more for the in-wall + the back box than a single good speaker would run you.