Based on duracoat; I've never cerakoted.
Aluminum Oxide gives the surface a little bite and increases surface area for the coating to adhere to. It's graded like sandpaper (60 grit gives a nice surface for outer surfaces IMO).
Glass Beads are more for polishing. If you had a SS barrel and wanted to keep it un-coated, bead blasting would be the way to go.
You'll need a large compressor to run a cabinet, so research before buying.