you'll get much better results with stainless in a shorter time than you will with dry media, however - if you're trying to process in volume, the HF rock tumbler isnt for you. the volume of the chamber(s) is just too small to do en-masse processing.
you may only get 50 or 60 rifle cases in there at a time, or less depending on the caliber.
tumbling time is 1-2 hours for good clean internals on your brass, so if you're trying to run 500 cases at a go, you could easily be looking at >10 hours of processing time for one batch of brass.
if you're a low volume reloader, its probably practical, but if you shoot in any volume - save up some more money and get the frankford aresenal kit.
it'll process 1000 223 sized cases at a time, has a built in timer (very nice bonus) and they usually come with pins too. they hit sale prices in the $160 range or so a couple times a year, so watch for them to come down and then if you can pair with a cabela's bucks deal or something and you're in like flynn.
i'm not unhappy with my thumlers at all, but if i had to do it again the frankford kit would be my choice simply due to volume and the timer. the model i currently have has a 12 lb capacity - so 5 lbs of pins, 5 lbs of brass, and a quart of water (2lbs) and i'm done. but thats still in the neighborhood of 350-400 pieces of 223 per batch.
hth