I'm not real sold on a flat trigger in a Glock, although I do have one (different brand) in my carry gun. YMMV, some guys like them a lot and it's really just personal preference.
I don't have any personal experience with that Overwatch trigger, but would guess it's probably just a different trigger shoe on a stock Glock trigger bar. Most of your trigger pull improvement will come from the "-" connector, but you might like the feel of the flat trigger too.
Just be careful to avoid triggers that claim to remove or reduce most of the pre-travel. (I don't know if the Overwatch trigger does that, but some brands do.) That pre-travel is one of the safety features of a Glock (it cocks the striker before firing) and IMO removing it is a bad idea for a carry gun. For a competition gun, have at it, just be safe.
