I ordered one of the SIG AIR sights right after reading the first post, as I've been looking for a cheap sight from a name brand that is readily available and likely to be of more consistent quality than no-name knockoffs. I'm pleased to report it is at least as good as one could expect for the money. Physically it is extremely similar to a sight I have that was sold as the Weaver Micro Red Dot Sight a few years ago, but thankfully the SIG has a much clearer tint. The SIG AIR uses the FastFire mounting pattern, though it would not fit something that was precisely milled for a FastFire due to the button on the front and different external dimensions. In my opinion this is better than the RMR pattern if you're going to be drilling holes in a blue gun, as the holes would not be so close to the edge of the slide. The SIG AIR uses a CR2032 mounted underneath the sight. The dot looks crisp and has 5 brightness levels. It doesn't get quite as bright as the RMR or Holosun but seems adequate. There is an elevation adjustment screw on top and windage adjustment screw on the right, along with two locking screws on the back. My experience zeroing a sight with similar adjustments on a .22 pistol a while back was not great, but it should be adequate for the intended purpose.

Below is a photo of the SIG AIR alongside a Burris FastFire 3, Trijicon RMR Type 1, and Holosun 507C X2. If you ignore the emitter housing hump, the SIG sits about 0.01" lower than the RMR and Holosun, with a window that from the shooter's perspective is just slightly larger than the RMR and smaller than the Holosun. The FastFire sits higher than the SIG due to its top-loading battery and has a window that is a tiny bit larger. Overall the SIG AIR seems like a good match to the RMR and Holosun for dry fire.