Is ova cue (ovulation predictor) usefull as a contraceptive? What is the best hormone free contraceptive method?

No and abstinence. The ovacue can predict ovulation but is not recommended as a contraceptive device. Abstinence is of course the best hormone free contraceptive. Next, condoms and devices such as IUD's. Good luck.
NO. abstain sexaully or double barrier: condoms, diaphragm, foam, sponge, spermicidal egg or-jelly. There is no "free ride"- if you are mature enough to have sex- you must be mature enough to protect yourself.