I had a 6mm Creed that would feed fine out of an AICS mag. I don't know if I had a unicorn or not as my sample size was 1 gun and 2 mags.
I have a CTR 260 and it feeds great with factory mags.
I have thought about switching everything to AICS mags just to keep things simple. Pmag's are a cheaper way to fly than true AICS mags. True AICS vs CTR mags are close to the same price if you look around some.
I have not done the swap to only one type of mag just because, if it ain't broke don't fix it, kind of thinking.
