I had the XS Big Dot (small dot is also available) installed on my Shield. I like "dot the i" sights the best. That is me personally. Sight is easy to find night or day with my old eyes. Rear sight post is not Tritium, but that does not bother me.
The Dot is designed to cover the target. Combat accuracy but my groups are not that much larger, if any, at 15 yards and less compared to normal 3 dot sights.
The big Dot is too tall to fit into my cheap Fobus holster. Also,if you have a tight custom holster, the Big Dot may not work.