Okay... I'll take one for the team and give my experience with it...
First of all, that exercise is called Kegal Exercise. Both men and women can do it for sexual performance. If you've ever had a really tight WG, and her pussy seems like it's milking your member, she might be doing these exercises.
I didn't stick with the exercise plan as discribed, I just did it every time I took a piss. Pee for a second, stop the flow. Pee another second, stop the flow.
I didn't notice a harder erection, or a longer one. Those seem to be more determined by how hot the girl is, and how tired I am. And Viagra and other erectile dysfunction meds can fix that problem.
What I did notice, was that I would shoot a little farther.
Also, with the muscle control, I was able to hold out MUCH longer if I wanted.
You guys know that point of no return.... when you go over the edge, and just think "TOO LATE! I'M BUSTING A NUT!!!!" and go all out?
After exercising for a few weeks, I was able to go over that edge for a bit, and just tense all the muscles, and pull myself back.
Now, I'm not saying I could last forever.... just that, a few times, I could hold it back, knowing that normally, I would have bust a nut.
This was just my experience with Kegal. YMMV
All you guys can stop giving me funny looks now....