Never used it, look up the speck sheets, the Ruby and Carared are nearly the same.
Just taking a glance at RedX and its a lot pailer, has live enzymes (about the same as a dark Munich) so you would need to be a bit careful doing a 1:1 sub as you could with the Ruby and Carared.
Red X is sold as a stand-alone malt. I've used it. On examination you see it's a blend of light malt and darker malts, the latter including a caramel malt and maybe a well-kilned Munich. So it's not a sub for Cara Ruby, which is 100% caramel malt and does not self-convert.