Works well for coupling 2 magazines, but could stand to have some minor improvemnts. - Caldwell AR-15 Mag Coupler

This coupler is largely designed to work with 2 5-10 round AR-15 magazines, but since it is angled, when used with those shorter magazines, you end up with a steeper angle than what you would get with a 20-30 round magazine. The increased angle does slow down the process of seating the magazine properly in the rifle, especially since you also do not have a completely flat base anymore in the way 2 magazines are coupled, thus a straighter overall profile would be more efficient.

Aside from the less than ideal ergonomics, the build quality is quite good in how it grips the ends of the magazines, especially at this price point.
Since we cannot do half stars, I would overall give this magazine coupler a 4.5 star rating, with what is needed for a 5 star being a less steep angle, similar to the first generation MagWedge couplers, and that is purely due to the design of the feed lips of the magazine and the angle that your hand will come in contact with it during normal use.

Overall, for the price, it is the best that I have seen so far.