It does what it suppose to do.
The DD A1.5 rear sight is an A1 style rear sight that attaches to your railed upper receiver. Instead of having the M16/M16A1 type aperture Daniel Defense uses the M16A2 aperture.
To install the sight you need to completely remove the screw that will hold it on. Then you slide it on from the front or the rear of the upper. You may need to remove your hand guard or your charging handle to do so.
The sight is very light and simple. The only complaint I could have about it is that the rear sight aperture is farther forward on this sight then on most other rear sights.
If you use this sight, keep in mind that the M16A2 rear sight aperture is not same plane, so the concept is to have a 300m zero on the small peep then the larger 0-2 sight will have a 200m zero useful for low light or moving targets.