For a rifle that with a Trijicon Reflex, as well as fixed BUIS, I now see that offset folding iron sights are available.

Having excellent quality fixed BUIS already, with lower third co-witness height, I am intrigued. Is it worth $190 for the folding offset sights that you must flip up to use? The obstruction of the fixed BUIS in the Reflex field of view is manageable, but not desirable.

Offset BUIS are not really designed for unmagnified optics that can cowitness. Sure, you can use them with that, but there's no real need to do so.

Instead, offset sights are designed to be used in conjunction with magnified optics, which cannot cowitness with iron sights. With a magnified optic, you either have to use offset sights, or detach the magnified optic altogether to use the BUIS.

In your case, stick with standard BUIS with your Trijicon reflex sight. If you feel your fixed BUIS are obstructing too much of your field of view, which with a lower 1/3rd setup they really shouldn't be, you could replace them with a set of flip-up standard (non-offset) BUIS.

Offset sights are great for rifles equipped with magnified options, but with RDS equipped rifles I stick with regular BUIS

Thank you all for saving me $184.99. Makes perfect sense.

I did absolute cowitness on mine (currently using a Holosun HS510C red dot), with the RDS on a quick release mount.