Very easy to install on my Specialized Allez and works surprisingly well. Not as well as a full coverage fender of course, but it keeps my butt and jersey dry on wet surfaces.
The fender's retention system adjusts easily for different seatpost diameters (unlike another brand I used for over a year). However, the sharp angle where the fender flares out makes it difficult to mount on shortslack seatposts. You can adjust the fender tilt upward so it doesn't rub your tire, but you have to do this in small increments to ensure the fender blocks all the road spray.
Quick and easy to attach and take off. It could pose a problem if you have your seat slammed, but then you probably have other problems, if that's the case. Takes care of the back spray, but won't protect you from rear spray around your cranks, find a clip on fender that can do that and color me impressed.