I do the same exact thing when I shoot my ak pistol. I'll warn the people next to me. I like when people give me a heads up but at the same time I realize we are in a shooting range so some guns will be loud.
I finally got to hold the carbine model recently and I really liked it, I'm trying to convince myself I don't need one haha. If I see an amazing deal it might be something I have to acquire.
^What he said, I have the Trijicon sights on my 17 and I love the big front sight. For me at least the acquisition is very quick and its super bright haha.
I recently read this guys reviews on the TA31, TA11, and TA33. It's pretty good write up, If I had to pick it would be the TA11 seems to be most ideal for all around stuff.
http://www.firearmreviews.net/acog-comparison/
My co-worker has the 3x30 on his patrol rifle, it works extremely well for distances you have described, he has the green horseshoe and I really like it. IIRC he picked his up for around $950 on sale, but I am not sure where.
I agree, it'd be a solid choice for a first glock. I've seen the magazines for sale so I may end up grabbing some of those, I'd like to have a few extra rounds.