every woman ovulates at different times, so if u want to stick to ovulation calendar method, she best get the ovulation kit or do it the old fashion way (check the temp. in her genitals) to find out exactly when she ovulates.

birth control or morning after pill.

there is no such thing as safe days, a girl can still get pregnant at anytime, highly unlikely at certain times but still a chance.
ALSO – there is such a thing called pre c.u.m and that would be before the male ejaculates, she is still able to get pregnant from that.
what you are doing as a "contraceptive" is not a contraceptive at all and there is still a risk of pregnancy.

the only PRO is pleasure, the biggest CON is a high chance of pregnancy