Funny thing about the JPoint (and the Docter and similar sights), I had one on my CZ75 SA and it was a disaster. Every time I drew, I had to hunt for the dot. Unless I made an efort to tilt the gun down, I was looking at an empty window. I finally took it off and installed it on my 10/22 where it works perfectly.
On the XDm, I don't have to hunt for the dot at all. It's always right there when the gun comes up. Otherwise, I wouldn't use it on my primary carry gun.
I'm assuming the difference is in the gun's grip angle and my physical makeup.
So, don't count on an optical sight working for you on any particular pistol.
Also, as strange as it might seem, I can shoot better groups with black iron sights than with the JPoint. The difference in group size is only about an inch at 25 yds. For steel or the plate rack or any other fast shooting, it makes no real accuracy difference and the dot sight is certainly faster to hit with.
I'd rather have the dot sight in a gunfight, because the dot is in the same focal plane as the target.