I've had some success rooting miracle fruit cuttings, using a relatively strong concentration of rooting hormone, bottom heat, and misting / 100% humidity, but as you said they take a long time (3 months or more) to root, and even after 6 months I've had many that stubbornly refused to root. Overall my success rate has not been high- maybe 10-20%.
Airlayering the stems to get the roots growing while still attached to the parent plant seems to be easier, quicker, and give a higher success rate for me, plus it allows for much larger cuttings.
Kevin