I kinda knew it before I purchased it....but Brownell's had them on sale, plus they were offering one of their "$10 off plus free shipping" deals...and I had a few beers...soooo.....yeah.....it cost me about $95 shipped.
I was finally able to take it too the Shoot Point Blank recently and it worked fine with no jams...BUT...
It is HEAVY when fully loaded. Holding up my pistol build started to suck when taking 1 shot ever few seconds.
It is a total PIA to load....big time. I hear it can be loaded with a certain type of speed loader and stripper clips. I hope so. I have a normal Maglula .223/5.56 speed loader and it does not work with the D60 as the speed loader is meant for double sticks, but the D60 loads almost like a single stack except you have to push a lever over for each round.
I've since reloaded it and put it away as a "SHTF" mag since it has rounds that I can't use at most ranges. Four rounds of 62gr green tips, followed by one 64gr tracer. I have two tracers in a row at the halfway point (rounds 29 and 30), and three tracers in a row at the end of the mag (rounds 58, 59, and 60). My guess is that I'll never use that mag...but, it is nice knowing I have it.
Final take: Works as described, but unless you have a bump-stock or something with full-auto......save your money and stick with 30 round mags.