From the paper:

Deutsch claimed to 'prove', via decision theory, that the 'rational' agent who believes she lives in an Everettian multiverse will nevertheless 'make decisions as if' the mod-squared measure gave chances for outcomes.

This must a bad wording, or something, otherwise why does a "rational" agent who does not believe "she lives in an Everettian multiverse" can still confirm the Born rule experimentally time after time?