They're a huge scam. They do NOT work.
The only way to actually "enlarge" the penis is expensive surgery to cut the suspensory ligament. This adds an inch or two to apparent length... and leaves the guy with an erection that hangs straight down.
By the way, women don't actually give much of a damn about penis size, especially given that we have very little basis of comparison... unless they're the sort not to be picky at all.

To the extent that it has ANYTHING to do with ***ual satisfaction, it's girth, not length. Really impressive lengths don't feel good, they HURT. "Wow! He's hung like a horse! I bet he could really bruise my cervix!"
The only people that truly care about penis size, in my experience, are guys.