This is a personal review of the XS BIG DOT Tritium Night Sights which I have had installed on my Springfield Armory XD 40cal 4 inch. Lets first take a look at these defensive sights. Here you can see why they call them "BIG DOT" sights. (Front sight) The rear sight seen here features a "V" shape with a single vertical line in the center. This is what the sight picture looks like, as the manufacturer describes, you just "dot the i." And finally here are the sights in total darkness, they are this bright in a camera, which means much brighter and easier to acquire for the human eye. Now that you have seen them, let me speak about the features. 1st: The tritium in these sights is SUPER bright, and the white color of them for use in higher light is very easy to acquire as well. 2nd: The "DOT" and the " I " The idea behind these defense sights is just that, use in personal defense. Situations where accuracy is thrown to the wolves and sheer instinctual shooting is the most reliable thing in the world. Forget red dot sights, 3 dot setups, and all the training and learning required to use them well, if the poop hits the fan and your mind can't handle the complexity of your aiming system, well then everything slows down while it tries to process, and thats when you are most vulnerable. These sights are so easy to pick up and put on target you could probably put them on a chainsaw and still be able to quickly sight it in. The idea behind this sight picture is you just simply put the dot on top of the line(dot the " i "), which also places the dot in the center of the "V" shape of the rear sight, giving you several different cues that you are on target. An important part of the overall design is the "V" shape of the rear sight. This "V" shape really reduces the possibility of covering the front sight completely with the rear thus "losing it." If you have ever picked up a strange firearm or ordered new sights and had to move the gun around in your grip until you finally saw both sights, that is what can get you killed in a life threatening situation. This "V" shape really reduces the occurrence of searching for your front sight, not to mention, the "BIG DOT" is freaking huge, so you would have to have the gun really off target to actually lose it. 3rd: The "BIG DOT" It is just as advertised, a big dot. The idea here is to have a very large front sight in order to decrease acquisition time and allow for simpler targeting. Another benefit to having a very large front sight is for people with failing vision, such as our older shooters, or, worst case scenario, a person whose vision is being impaired due to an injury sustained during the fight. Think about this for a moment, if you cant see your sights clearly you can't, safely, take the shot. 4th: Accuracy? So many people have written and theorized and argued that these sights are less accurate than more traditional sighting systems like the 3 dot sights. This may be true for some, but it is definitely not true for many. I was blown away with how accurate I could be with these sights. Even if this happens to be true for you, remember, these are defensive sights, not bullseye sights. If you can hit a torso sized target at up to 25 yards, they are doing exactly what they are meant to do. Besides, good luck convincing the judge you "had" to shoot a guy who was further than 25 yards away from you, yes there are potential scenarios when it might be required, but most of the time you can either run away, or close to a more accurate firing distance. Even if you happen to fall into this one in a bazillion situation, then do exactly what you would with a 3 dot, focus on horizontal alignment and instead of aiming with the center of the dot, use the top as described by the manufacturer for shooting at targets greater than 25 yards. Oh and guess what, horizontal alignment is a cinch with these, how many times have you ever 2nd guessed your 3 post sights because you couldn't tell whether the gap was equal on both sides of the front sight....? In my opinion, these sights are just as accurate as the factory 3 dots they replaced and much easier to aim instictively, so that means "more" accurate when it counts. If you want to shoot diamonds out of aces at 25+ yards, then you shouldn't be using defensive sights period. Overall opinion of the XS BIG DOT NIGHT SIGHTS: A+, 5 stars, 2 thumbs up, and hopefully I will never have to write a story about how they saved my life, but if the time comes, I'm confident they will.