I just installed a 507C onto my Glock 19X and took it shooting today. After about a mag and a half of shots, I had it dialed in. After that I was punching out the center and the area around it with entire mags. It was so easy. It was a very enjoyable range visit. I commented to one of the guys as I left that shooting with a red dot is almost cheating. Put the red dot/circle where you want to hit and it goes there. I loved it.
This was actually my first time I have been able to spend any real amount of time with a properly sighted red dot on a pistol. It was really fun and has made me much more confident with my shooting. I think everyone needs a red dot on their pistols!
I am sold on Holosun red dots now. Good luck with your sale. I would have bought it if you had posted it for sale about 3 weeks ago.