The claim by xssights.com is that their gun sights  are "the finest sights made for fast sight acquisition in all light conditions." Is this so? Can anyone compare this or other 'dot the I' replacement sights? My gunsmith is not convinced?

I used 3 for sights for many years and ran across the XS during a class as TacPro in TX. To me they work well and while under pressure you are not going to really line things up and "aim"… the big circle does make it very easy to pick up the front post for a quick reference. They clearly say they are NOT target sights and not designed to shoot through the same hole over and over. (Though you actually can with practice.) When the tritium finally wore out on my carry gun after about 15 years, I swapped over to the XS. I prefer the white line in the rear, not the tritium vial because I get a faster sight picture. (Personal preference.) I can also reliably get hits on my IPSC steel target from 50 yds using the big dot sight on a medium frame .40 S&W Glock (23).Honestly I think it all comes down to training and practice. If you shoot enough rounds you can be proficient with almost anything. I changed over my two carry guns (23 & 43) last summer and have about 3,500 rounds through the 23 and 2,000 rounds through the 43. I feel confident that if I need to defend myself or my family, then I would be able to do so efficiently with these sights. If I didn't, I would have gone back to the 3 dot ones I used to have!!!  I would recommend trying them out. The customer service I have gotten calling the company has been a solid 10 out of 10 too!!!No matter your choice, get some good training for the basics and shoot as much and often as you can!!!  A year ago I moved where I now have a 50 yd pistol range and a 100 yd rifle range at home and my skills have improved 10 fold due to the frequency I get to put round down range!!!  If that isn't an option, the laserlyte system works good too… especially when doing sight acquisition drills. (Not so much on follow up shots.)Not sure if that answered you, but I hope the info helps.