FYI, the PADS rear flip sight has a loose retaining pin and I wouldn't spend the money on it.
We have been running them on our M4's and every single one of them has had a problem with the retaining pin slipping out and allowing the sight to flip up with a slight bump. Well our M4's get bumped a lot so the sight is flipped up all the time and won't lock down until you pull out a gerber or pocket knife and push the pin back into place. Not something you want to do while in a fire fight.
The range adjustment knob is also always off of zero and had to be put back even at the range when we were zeroing.
Here is a picture of the sight from RRA website.
[This message has been edited by CT'97 (edited 2/17/2008 9:40a).]