I finally broke down and got a blast cabinet for doing rust blueing.

What is the basic difference (characteristics, desirable or otherwise) between using glass bead and/or aluminum oxide abrasive for said task?

I don't know anything about it, but thought I would offer this word of caution since I read about it just this morning. silica be breathed is one of the most dangerous things you can breathe into your lungs so if you use an abrasive that has 1% or more of silica you should (this i guess would apply if you weren't using a sealed cabinet) wear a hood with its own air supply and change out of the clothes and wash thoroughly before going into the house or touching your mouth, eating etc. etc. you get it.

It was in some magazine I have. Handy or something like that.

Red

The aluminum oxide is used by the tactical guys for a rougher finish. I use glass for rust bluing and it gives a great finish.