Well, this brings up the question: which kind of "red dot" are we talking about? There are the reflex ("tombstone" types, there are the small (1-inch, plus-or-minus) tube type, and there are the 30mm to 40mm tube type.
Which type? And do you have a budget?
I'm a beginner at target shooting and I've tried a few different options at the range, where other shooters let me try their sights. At this point I want something that will be accurate at 25 yards and easy to use indoors. I'd like to stay under $100 if possible since I already spent $350 on the gun.