Two of the characteristics you look for in a home defense shotgun are simplicity and speed. Should you ever need the gun to perform its primary duty, you need it fast, and you need it easy.
The simplest possible sight for a shotgun is what most of them already wear – a single bead out on the end of the barrel. This is a fine choice – make that, the best choice – for wingshooting, which is more about instinct than it is precision. However, acquiring and honing the necessary skills for “instinctive” style shooting requires a great deal of training. For example, you need to drill and drill and drill on mounting the gun into the same position every single time.