They are both butch animalic leathers, but there are differences.
Rien is a powerful, almost disturbingly so, dry leather with tons of animalic musks. No woods or smoothing ambers. It's like a big living animal. Leather oud smells like smoked oud, a combination of woods, resins, leathers, and some animalics. A leather, but less directly so. The drydown is suitably dry, but less so than Rien.
While it's quite butch, it's certainly more refined and elegant than Rien; you wouldn't mistake it for a living animal. So if you thought Rien as being rough, or simplistic, Leather oud will likely have more interest and variety. So I think you shouldn't exclude it a priori. Of course, at those prices, you really need to sample. Incidentally, the drydown of Leather Oud is not miles away from that of Oud Ispahan, though the way to get there is completely different. OI starts as a metallic rose. In any case, if you like the base but want something different than a butch leather, it's something you can consider as well.