The one I use is called "The Perfect Penis Extension - 9"" by Deeva which is just a hollow tube with a penis shaped detail on the outside held on by straps. I am 5", and I LOVE using this toy, as my FWB's have as well (one straight and one lesbian even!)
In regards to your comment "sex must be pleasant for both parts", I think it should have been followed up with "for me".
For myself, the brain is the biggest sex organ, and even though I have no physical sensation on my penis while wearing this, it is watching the girl's reactions to being completely filled that turns me on beyond belief, and I have cum every time that I have worn it.
