Well, it's fair to say .cdi can be dirty, i agree, it's a .gdi rip after all, who knows who made it and what did he cut out/compressed. But most of them are good and almost ideal copies to gdi's. Anyway, there's no doubt the best way to go is either .gdi or chd.Actually CDI is dirty and its only propurse is to run backups on real hw, clean redump format (GDI since redump moved to CUE format) or converted CHD is always recommended for flycast.