I'm not real familiar with magnesium but when I was powder coating the consensus on the powder coating forums was stay away from glass media. It has silica/silicone and is not good for prepping parts to be coated. Same thing as leaving silicone wax on a part then painting it. That may only apply to the guys who are looking for perfect finishes but do some research and decide for yourself. I always used aluminum oxide and I coated a lot of condemned titanium and mag helicopter parts for setup. I use the HF cabinet but sealed it on the inside and out with a 2 part sealer. I also fashioned a deflector on the door to keep media from piling up on the ledge and falling out when opening it. I also just used a shop vac with a filter bag on the inside. It did ok, not great. I threw away the HF gun and used the TP tools replacement with carbide tips. Also grab their gloves, they are 10x nicer.