Alpha is decent for breathable insulation, but I would avoid it if you are using a wind resistant shell for any application. Go with Apex for a quilt, definitely.
Warmth to weight: the clo value of Apex is .82, whereas Alpha is between .28-.37 (depending on the weight of the material. not sure why it changes, but that is what is reported), so 60g Apex is as warm as 120-180g Alpha.
Cost per linear yard (60″ bolt): Alpha 90gsm is $9.95 at mill yardage. Apex 2.5oz (~85gsm) is $7.00 at ripstop by the roll. so 2-3 times the insulation value for 30% cheaper. that site also has recommendations for making quilts with desired temp ratings (2.5oz for 50* all the way to 7oz for 10*).
For active clothing, Alpha has its place. I have 80g Alpha in two pieces (both feel closer to .30, so not much warmth for the weight). I love one jacket because it breathes well and has a burly face fabric with good stretch. great for climbing, but heavy. the other has a wind resistance shell, so it does not breathe as well as the insulation is intended, and is not very warm, so I never use it. I prefer patagonia full range (.56 clo–nano air line) or arcteryx coreloft continuous (.80ish–proton lt/ar) for highly breathable mid layers.
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