This must be they ad in "Shotgun News" they are referring to.
People buy those DIAS'es and find out that it's not a solution for several reasons that I won't list here. In short, it's not enough.
LOL. This won't work. You'll need an entirely different bolt among other things.
There were some in circulation before the BATF and Congress tightened things up in 1981, and these were grandfathered in, so it is possible to buy an unregistered drop in auto sear. However, the legal unregistered ones are 1) expensive, 2) illegal to own if you also possess an AR-15 rifle or even certain combinations of AR-15 and M-16 parts, and 3) don't fit in most newer AR-15 guns anyway, as Colt modified them to prevent using the DIAS device back in the 80's.
-ccm