from my personal experience , aluminum oxide last a bit longer , the black diamond last about 4 cycles . maybe a bit more . i use a pressure blaster in a cabinet and it works great . and leave a heck of an "etch" or the coating to adhere to .
when i was buying aluminum oxide it was like 40.00 for 50lb , the black diamond is like 7.00 a 50lb bag ., kinda a no brainer if you live close to a tractor supply .
or go to there website
ATI - Black Diamond i think they may sell whole sale but did not try yet