If you don't have a "life threatening" job for your AR, they work just fine. Mine has been reliable for three years of weekend shooting.
I purchased mine before the one with the included riser was available and I've heard that the riser isn't at the best height, but then again I haven't tried it. See if the riser works for you, and if not, invest in one of the UTG risers, it's not a high stress part.