i have a couple sand/beadblasting setup's, one is just a large gravity feed system used for doing truck frames and bodys and large stuff and i have an enclosed setup for smaller stuff. the gravity feed one works well, but it makes a huge mess, and you'll be picking that crap out of places of your body you don't want that stuff. but both do the job i prefer sand because it's much cheaper, and both you can reuse more than once but after a few times it takes alot longer. that one mentioned for 12 bucks, does the job of a 12 dollar blaster, it'll take you the better part of the day to do one valve cover. to tell the truth i have just used a 3 1/2" grinder with a wire wheel to do valve covers and then just painted them.
shawn