I have a kydex sheath for my AR (also from Matt D, & I will also 2nd the great service/price comment). I hadn't seen one prior to buying it, & was a little sceptical about how well it would work. I've been using it for a couple of weeks now, and am really pleased with it. I wear it horizontally on my right side. It is very secure, yet allows the knife to be drawn & inserted easily, plus saves quite a bit of wear & tear on the pocket.
Rick