My late Father used the original Ferraniacolor (25ASA) was the first film easily processable at home (kits were made by Johnsons of Hendon, one of the major suppliers of B&W chemicals for the UK. I'm sure it was based on the Agfacolor system of that time. The Dia 28 was a later introduction (I think 50ASA), and, IIRC, sold in the UK with processing included when you mailed in back to the manufacturer's UK lab. Again, I'd think it was just an improved version using the same Agfacolor system.