It might as well be KVO under the hood, no problem. It's just that annotations can be really handy to indicate a ton of stuff that would otherwise be lines of code. I use it in other languages all of the time.
yeah, I'll agree here. Being able to slap an annotation on a method in C# is one of the major pluses. [Authorize] in ASP.NET MVC (Core as well I believe?), the various ones in Entity Framework, etc. Very useful.