As above. You're better off buying separately, you then have full control over which products are in your mix.
Many people will tell you that you shouldn't mix AC with GFO and I was one of these for a long time. However I saw that they do exactly that in their hospital tanks at the national aquarium in Noumea so I started experimenting. I now mix them all the time but it takes some fiddling to get the combination right for your tank.
You need really good quality granulated active carbon (not pellets) and you have to get the percentages correct or you waste product. It's probably easier to run them in separate reactors however for me personally, I found that mixing them prevents the GFO from channeling, settling and clumping. Most reactors tell you to open the flow to full once a week to prevent these issues and that works. I'm just into simplifying maintenance so combining them works for me.
However with the wrong carbon it can grind and turn both your AC and GFO to dust which may get into the display. My proportions may not work for you but I run about 1 part GFO (Rowaphos) to 2.5 parts AC.
This explains a little about different carbons etc.