i like them. i dont use them at night, but during the day, they are great to keep all the swimmers from dripping out all day as you walk around.
i have to say though, i was very comfortable with using them because i used a diaphram for bc for a couple years, and by coincidence, the instead cup is the exact size of my old diaphram. so i had no trouble inserting/removing, and it fits me just right. if you dont have any experience, i would definitely try it out before crunch time, because it could take some practice, and im not sure how well one size fits all. i also use preseed with it just like you would use spermicide with a diaphram- a dollop in the middle of the cup and around the edge, just to give a little pH balanced support to the sperm while it's in there, just because, well, why not.