They are awesome. Very light, you can feel each other as if there were nothing there, however, it can be difficult to insert the first time. Some women prefer to do it alone and sometimes couples find it fun to do together.
The package comes with instructions. She needs to squeeze the inner ring until it looks like a figure 8 and then slide it into the vagina pushing the bottom edge of the ring toward the bottom of her cervix. This is tricky because the sheath is lubricated and therefore slippery.
Once it is pushed in she can begin to tuck the top of the ring in to fit over the top of her cervix. Then she should insert her fingers into the sheath and feel around the edges to ensure the ring is sitting snugly, otherwise it can pinch if it's not flush with the cervix. The sheath will hang out of the vagina, looking like a deflated balloon, and that is the only drawback: it looks dorky. When the penis enters it takes up the slack.
Remember, the cervix sits on a slant, the bottom is further in and the top is tilted out. Check out the diagram on the insert of the package. Make sure you use lubricant; they provide small samples with the product.
Upon researching this product I discovered it has a big following with gay men. If the inner ring is removed it can be tucked into the rectal passage. This protects not only against STD's but, also protects the thin tissue of the rectal passage. With both the vagina and the rectum lined with a fem condom a man can do the ole 'double dip' without worry of transferring bacteria from the rectum to the vagina. I've been told that if the condom slips inside the rectum it will come out with the next movement, or with a douche of warm water. (this is anecdotal! no research to back that statement up!)
The best thing about this condom is that it can be inserted well before intimacy, and you don't need to change it until the end of the session, so although it's initial cost may seem high, you are using one female condom to a ratio of 3 to 4 male condoms depending on your mileage.
Enjoy your evening!