I'm not up to date on what is cast v. MIM, but the gas key and extractor have injection markings of some sort.
I thought MIM was superior to casting for small parts, especially those with complex shapes like the gas key. The MIM process seems kind of ideal for the gas key, where precision and lack of defects would be paramount.
I think an extractor made from tool steel (which I believe the spec calls for) would be better, as it seems that part would suffer from quite a bit of wear and need to be fairly strong. I have read that spec calls for S2 tool steel for the extractor and pin, but I guess that is bascially unobtanium unless you order like 12 tons of it. I know some manufacturers are using S7 tool steel. I'd probably rather have that than a MIM or cast extractor.
The AIM bolt seems pretty nice for the price. Whether that is good enough is pretty much impossible to answer. A bolt could be made of the "wrong" metal and we would never know it. Maybe the "wrong" material is 99% as good as the "right" metal - or maybe the "wrong" material is actually better than the "right" stuff (as may be the case with C158 v. 9310 bolts). Or maybe it is the "right" metal, but it is heat treated improperty. That is probably more critical than what type of steel it is. If you are not buying Colt (or maybe the one or two other manufacturers who 100% follow spec) you are taking a risk. The nice thing about buying from AIM is the reasonable price and the fact that they will stand behind their product.
I thought the staking looked fine on the AIM bolt I received.