I have used the Female Condom2 model, the one made of Nitrile rather than polyurethane, with three local ladies. Two of them had not used a Female Condom previously. None of them had any trouble inserting the device. One stated that it diminished her perceived sensations somewhat and speculated that "this must be what it is like to wear a (male) condom". Perhaps, that is really hard to know. There were no problems with the FC2 staying in place. These nitrile version are "quiet" without the rustling or crinkling sound of the polyurethane originals. Either should work for people who are allergic to latex.
Where the FC2 shines is in doubles where the customer guy can go from one woman to the other freely without changing condoms. That easily justifies the additional price, IMHO.
As far as the "80% effective" figure VictoriaLynn mentioned, that is in preventing pregnancy in couples consistently using the method over a year's time. It used to be said that male condoms were 80% effective, then studies with more highly motivated users showed a 90% effectiveness and a trial where all the male users were M.D.s reported 100% effectiveness. In other words, like seat belts and personal floatation devices, condoms only work when they are actually worn. Wikipedia's article
http://en.wikipedia.org/wiki/Female_condom
puts the FC's effectiveness at 95% with "perfect" use and 79% with "typical" use.
This article from the Journal of Epidemiology
http://aje.oxfordjournals.org/content/166/1/88.abstract
compared male to female condoms by measuring trace presence of PSA (Prostate Specific Antigen) in the woman's vaginal fluids after intercourse. PSA could be detected in 3.5% of cases where a male condom was used and 4.5% of cases where a female condom was used. Not much difference.
As someone who has not ejaculated inside a condom in this century I can't help wondering whether the combination of all condoms, all of the time (except for idiots) for intravaginal sex and typical extravaginal ejaculation whenever he can negotiate it doesn't lower STD transmission rates in the Hobby significantly below condom usage by itself?
BTW, the FC2 is available from Amazon.