If you do an internet search for "red dot footprints" in a, you'll get a lot of info pop up. I found a bunch doing that, just didn't save any of them after I read over things.
You do need to make sure the dots footprint will work with the gun you have or how its set up.
Trijicon RMR's footprint seems to be a pretty common one, and some of the other makers, like Holosun, have sights that use the same footprint. I went with that, as I was originally intending on getting one of the RMR's, but after getting one of three Holosun 407's to try out, Ill probably stick with that for now.
Holosuns SCS-MOS version takes things up a level and goes on the Glock MOS without a plate and you can use the factory irons with it too. Looks like they are making them for other guns now too. Im thinking they may be the way to go going forward. I put one on one of my 26's and like it.
I tried one of the plates that replaces the rear sight and uses its dovetail when I was trying to figure out if I wanted a dot on my 26. The plate I used was from EGW, and it worked, but I didn't like how or where it put the dot on the gun. It validated the idea for me, but I knew there were better options and I went that route.
If you arent sure if a red dot is what you want, it might be an option to try it and see, but after going that route, I don't think its the best way to go.