The QiYi Super Ivy Cube is the same puzzle as a Rex Cube, but way better than the Meffert's or LanLan Rex Cubes. I'm pretty sure most FTO speed solvers use the Super Ivy modded into the RexTO, so I wouldn't put it in the bad hardware category.
Rex Cube is also not that easy. It's like a simplified FTO shapemod, and both Rex/FTO are one level up from the pyraminx/skewb. They're more like 3x3 in complexity.
I hope the FTO is added next as an official WCA event. Aftert that, the Rex Cube would be sort of redundant. I'd put all the shapemods into the "existing puzzle" tier, really.