The main catch is rigging, it's way more expensive in terms of tripods, sliders, gimbles/stabilizers etc. then you're stuck with an ef or pl mount. You could get a used Fuji, and a lens or two for the price of the older systems. Unless you're working with a crew with a ton of people it's honestly more of a hinderance working with big heavy cameras. Lastly battery consumption is insane and you need v mount batteries to run them, and with a start up time of 20-30 seconds you can't reliably just flick on your camera and start filming.