Not as good as other. If 100 couples use spermicides alone for birth control for a year, 28/100 will get pregnant in typical use. Even if used perfectly, 18/100 will get pregnant. There are many other more effective methods of birth control. See http://www.Contraceptivetechnology.Org/table.Html for a chart showing contraceptive options from less to more effective.
Spermicide . Spermicide is not a great form of contraception by itself. The failure rate is a bit too high. And remember, spermicide may not completely protect against sexually transmitted infections either. However, used in conjunction with condoms, spermicide is a very effective form of contraception and helps protect again sexually transmitted infections. Many condoms brands come with spermicidal lubricant included. If you are trying not to get pregnant, you really want to use something that give you the best chance to not get pregnant. Some options for that are: iud's (intrauterine devices) which are small pieces of plastic or copper that are inserted into the uterus in the doctor's office with minimal discomfort and no anesthesia needed that can stay in for 5-10 years and be easily removed if future pregnancy is desired, a vaginal ring that you yourself put into the vagina once per month, a contraceptive patch that goes on the skin. There are also permanent procedures including tubal ligation (tubes tied) for women and vasectomy for men when people are done having all the children they want. There are also a bunch of different kinds of birth control pills that are highly effective if taken correctly. There are a few other ones as well, but aren't used very often.