Both are diffusion type filters but DIFFUSER gives a soft-focus effect due to its irregularly uneven surface while DUTO has fine concentric lines etched on its surface.
The center of the picture is usually sharp with DUTO but DIFFUSER gives an overall soft-focus effect.
Both are particularly effective in portraiture and commercial photography.
In order to avoid purchasing one of those counterfeit filters we highly recommend to purchase only from official retailers that are recognized by HOYA's official global distributors. Prior the purchase kindly inquire and verify whether a retailer is authorized by HOYA global distributors. You may find the contact in the HOYA global distributors list.