We use Mimi during intercourse sometimes. It works best in positions where our bodies are pressed together holding Mimi in place. WOT works if I lean forward a bit. Some variations of missionary work. We often use position pillows for doggy. For this, I can put Mimi between the pillow and my clit. As long as I stay pushed against the pillow, Mimi stays put. Granted sometimes Mimi slips and I need to move her back. Some positions require Mimi to be held in place.
My body responds best to indirect broad clitoral stimulation. So I'm not limited to the toy being in just the one perfect spot on my clit. I can place Mimi in the general area and get all the stimulation I need. If she starts to slip chances are it's still gving me enough broad stimulation. Mimi might not work so well-at least handsfree- for someone who needs direct stimulation to the clitoris.
Having said all that, Life works better than Mimi. The shape contours to my body easier. I don't have much slippage with Life at all.