It is no different at EK. Days off downroute can be used to satisfy legal requirements i.e 1 day off in 7. But regardless of how many days off down route you have, you are still required to have a min of 7 days off at home in any given month and an average of 8 over a 3 month period.
I would wager that the J* deal turns out to be better than EK with regard to guaranteed days off at home.