What I read.
Statistically they are very close to as effective fro birth control as condoms when properly used. They are supposed to be slightly more effective on some STDS (I think it was herpes).
I've used them a few times, and for my part they feel fantastic!
I would much rather use the female condom than a normal one. It feels closer to bare back. Unfortunately in my experience, some SPs won't use them.
The only draw back for me is the cost, but its just a few bucks.
