What is the advantage of them, compared to an a/c/c arrow?
Looks to me like marketing more than anything else. I do think they might be a tad easier to pull out of targets with the aluminum exterior. There is a possibility they could hold their spine longer but I think that is open to debate. Perhaps they would be more abrasion resistant.
Their specs aren't any better than an ACC.
Axis Full Metal Jacket...Straightness: +/-.003"
Weight Tolerance : +/- 2.0 grains
ACC and/or A/C Super Slim.....Straightness; +/-.002"
Weight Tolerance: +/- .05 grains