Image quality test results have been added to the Rokinon SP 50mm f/1.2 Lens page.
I'll get you started with a comparison:
Rokinon SP (Samyang XP) 50mm f/1.2 Lens compared to the Canon EF 50mm f/1.2L USM Lens
The Rokinon SP 50mm f/1.2 Lens is in stock and on sale now at B&H (save $350.00 instantly)| Adorama | Amazon USA | WEX