Personally, the only thing iRay seems to have that Superfly doesn't is micromesh displacement - a feature requested here to exhaustion, that's been included into Blender Cycles already. I have no idea how iRay materials are built, so I can't speak for ease - Cycles materials are pretty easy, and Superfly also takes regular Poser materials and Physical Surface.

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Feel free to call me Ohki!

Poser Pro 11, Poser 12 and Poser 13, Windows 10, Superfly junkie. My units are milimeters.

Persephone (the computer): AMD Ryzen 9 5900x, RTX 3070 GPU, 96gb ram.