There are many excellent sights on the market for target and long distance shooting. They narrow your vision for long distance accuracy - if you have the time, opportunity and clear field. In other words, they are great for the 50 yard range.
But in defense shooting the space is closer, the time is shorter, the adrenaline is rushing into your bloodstream and tunnel vision is kicking in, and you may have to deal with the distractions of one or more BGs, bystanders and your environment (field) for a clear and safe shot.
The AO Big Dot Sights allow you to place the front sight on the target quicker than other sights. Also, the rear sight opens up your vision better than any other sight I've seen. The AO Big Dot Tritiums are the best sights for concealed carry and shooting.