I tried some electric stimulation before with a lady friend of mine that is a dominatrix.  It was very nice, intense, but not to the level of the vids I think you are referring to.

I enjoy it and it can be quite pleasurable.  With the right electrode it makes your muscles twitch and feels kind of like vibrations.  I have some conductive rubber tubing that I can use with an inexpensive controller and sometimes achieve a hands-free orgasm.  The key is using an electrode that distributes the sensation enough and having a controller that will let you customize the setting enough.  You also need to use plenty of the electrode gel to eliminate any hot spots.
Once I had one slide off and that hurt like hell.  If there is only a small area of skin touching the electrode it will be really intense and actually feel like you are being shocked, which I personally do not recommend doing to your member.

I got the conductive tubing on happystim-usa.com and the controller on Amazon.  I'm sure if I got a controller actually built for this it would be more customizable and better, but I didn't want to spend the money since I didn't know if I'd actually like it.