I came across this video that covers the Holosun current line of red dots.
I only have experience with the 507c, 507c-x2, and 507k-x2 but it is all been pretty good. I still use Burris Fast Fire 3 3moa dots on my P-09 and 97 pistols and my only complaint with the Burris is not enough dot brightness adjustment steps. The Holosun's have maybe 10 or 12 clicks in adjustment, and I routinely adjust the brightness on overcast gloomy days, the Burris has 3 and I wind up with the dot too bright or too dim on gloomy low contrast days.
Joe