I was thinking about getting some sights to back up my red dot on the 9G carbine I'm putting together. My question is this: is there any advantages/disadvantage with fixed sights compared to the folding battle sights? I see that the fixed are cheaper (less parts I guess) but there would be a certain convenience with a "flip up" sight.....but one opinion I've heard was that they were not as durable once they were drug through the dirt a bit, i.e. the moving parts failed after dirt and other particles penetrated the moving mechanism. Any opinions formed through practical application?