Range and carry guns. Glock 19 Gen 3 and a Sig 365XL.
For the P365XL, I think that you are going to be limited to Holosun, Sig Romeo and, maybe RMSc if you want to use the integral cutout on the gun without any additional modifications and/or adapters. The Holosun models appear to be the best according to forum-land. The Sig version doesn't really get good reviews. I have 507K-X2s on a P365 and P365XL, and they are doing well. However, there are some nuances to consider that I wish I had known before buying.
The 507K allows switching between 3 reticle choices, which are circle + dot, circle only, and dot only. The dot is a 2 MOA dot, which is rather small. When using the dot only, in order to see it in bright daylight conditions, you have to turn it up and bloom the dot. This works during the day, but it really creates glare in low light when leaving it on the day setting. If you like the circle + dot or circle only, there is no need to bloom the dot and it works out ok. The problem is that I have learned that circle + dot and circle only are too busy for me, especially when shooting smaller targets. I like the dot only. Another problem is that the placement of the + and - buttons on the optic, which turn it on and off when pressed simultaneously, has resulted in my turning the dot off while racking the slide with my fingers on the buttons. This has caused me to use the lock-out feature to prevent that from happening. This makes it more difficult to change dot settings on the fly.
Holosun also makes a 407K, which is a 6 MOA dot only. If you want to use the dot only, you get a bigger dot without having to bloom it. It is about $100 cheaper. I also understand that there is a green dot version of this sight that brings up the cost a bit more.
You may want to settle on a preferred reticle and/or dot size before buying.
As for the rudimentary backup sights on the 507K/407K, you just have to learn the proper sight picture. For me, the shallow "backup" rear sight does not allow me to use a traditional sight picture on either gun.
YMMV.
