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I have the Big Dots on my XD45C and my G30SF and I love them. I can still hold tight groups at 25 yards with them. They take a little to get used to if you're used to the three dot system. Your shooting will be off a little but after a few mags you'll be doing good. They use Trijicons vials in them so they glow nice and bright.
If your a target shooter you won't like them. However, that's not what they are designed for. They were designed for quick target aquisition perfect for a defensive pistol. I would highly recommend them and will continue to put them on my carry pistols.
I would stay or run away from the TFO sights. Just go to the XD forum and it won't take long for you to find a thread about how the fiber optics fell out of the sight. Those sights can't stand up to abuse or use. I would restrict their usage strictly to a range pistol.