1. They are fairly difficult to use. For some odd reason, I can never insert the ring into my vagina. I always have to take out the ring, stuff the FC in my vagina, or insert it in via a dildo or hard cock.
2. I don't offer CBJ, so I really can't say.
3. Put a LOT of lube on the inside of it. Oh, and use the "warming" kind of lube. A warm sensation will give the condom a more "natural" feel.
4. I love using FC because they give the vagina "less friction" sort to speak. My girl can become easily irritated with the regular condom, and I like to use FC's instead. However, they can be very expensive and many sex shops don't carry them.
Also, my guys who tend to go limp when the cover goes on like these as well.
Hope this helps! Have fun.