I got the holsun 507c green for my FNX-45 tactical. I'm still practicing and learning to adapt to self-defense RD, but I LOVE the circle dot. I'm thinking about an RD for my 365XL as well, and definitely want the circle dot option, but the 507c seems a bit big for the 365.
I upgraded to circle dot RDS on my rifles as well.
I have the Holosun with the ACSS huge circle/ dot, but it's not installed yet. I was going to put it on a P80 G19 long slide I have to build, but I might put it on the new G17 I just impulse purchased. We'll see.
I have a Burris Fastfire 3 on a P80 G19 and a holosun 507 on a 10mm P80 that I've played with, but the bulk of my RDS pistol time is on a (different) p80 G19 that I run and gun with, and my 365XL that I CCW. The G19 has had a Seampfox Kingslayer, and now has a RMR, and the Sig has a Romeo Zero. Circle dot is nice, but I find just a dot (or chevron) to be just as good at pistol ammo out to 50ish yards. As with any shooting discipline practice is important, but once you get past the early couple hundred rounds of relearning focus, the difference is stupid.
At run and gun, the guys with sights (who are good shooters) are always behind the optics guys. And usually whole seconds back.
IME the key attribute of a pistol optic is window size. The bigger the window, the sloppier your presentation can be and still have a reticle, but even the smallest windowed red dot let's you have way worse presentation then a sight and still see. Which reticle it is is a distant second,
Ben:
The 507c is an RMR footprint and won't bolt to the 365xl directly. You can bolt up a Romero Zero, Shield RMSC, or a Holosun 507
K series. I haven't played with the k series directly but it seems a little taller than the other two. Still under an inch to fit the slide though.