two very different systems. the X gives you the option to run as a solo plate and control the rifle by grabbing the plate and the bag at once (hence the thumb rest on it). where the orig railchanger is more of a way to just carry the gamechanger around.
in my opinion, if you want to be able to attach a gamechanger size bag to your rifle, the X is the way to go. it attaches much more securely and give a better overall package. (fyi, might need to take some fill out of the gamechanger for best results)
I use my railchanger with the small sticky bag mounted on it. That for me is a specific use product. i use it on unstable barricades and use a tripod for rear support, so things like cattle gates and other pipe props and rickety things that we have to shoot of off. Using the railchanger in this way allows a small lightweight bag that doesn't slip to be attached to the rifle, keeping a hand free to manipulate the tripod.