There is a bit of a learning curve with them, you have to get used to focusing on the target and not the sight, it's a fundamental change but one that makes sense as something you would want to do if you think about it, you're no longer looking at a blurry target and an in focus front sight or vice versa.
If you go with something that doesn't co-witness with the iron sights you will also have to make some adjustments on how you present things or will find yourself searching for the dot.
I pretty much budget in an optic for everything new I buy these days. Of course I'm also getting old, and need my TopFocal glasses to clearly see the front sight these days, so that's also a part of it.
On the question of reliability, I do have to admit that it is something that can break, especially compared to two pieces of metal on a slide. For EDC I spend the extra money on Trijicon RMRcc's for the reliability (and I will admit to being a bit of a Trijicon fanboy.) For the range guns I'll put pretty much anything on one, usually staying with established brands, but also have some of the $50 made in China clones, that I usually put on air guns, mounted on the rimfire stuff, and as experiments to see if the thing will survive on a center fire pistol.