I've tried them a few times, and haven't been overly impressed. I thought they would be useful for men who were more well-endowed, as they don't "strangle" the penis like traditional condoms. I thought they might also be useful for someone having difficulty maintaining an erection long enough to put on a condom, or just for increasing spontaneity (I could put it in before we start, thereby eliminating the need to take a break to put the condom on). There is also a small amount of external coverage, which helps to decrease the risk of contracting certain STDs (i.e. genital herpes).
First of all, they cost about $5 apiece. Pretty steep, in my opinion. Second, they feel really weird and unnatural inside, not unlike a glad sandwich bag. The feeling was a real turn-off for me, and I believe it was for the unlucky gentlemen as well. If you don't put enough lube in them, they have a tendency to ride the penis and come out any time the man pulls out. Overall, a waste of $15/3, as I had a 0% success rate with them.
L/A/S 0/3/0