The Demon carbs are just massaged Holley's, nothing new. Most of the parts are interchangeable. Barry Grant got his start tweaking Holleys much the same as Proform or Quick Fuel and just evolved into manufacturing his own version of a Holley.
I have a 725 Road Demon and it's the worest carb I have ever tried to tune, constantly chasing it. Got so frustrated I went back to a basic Holley 4160 600 cfm carb, tweaked the main jets and set the idle mixture and have not had to touch it in two years.