rock is rock. even if it isnt in good shape now, it'll be fine once in the tank for a few months. i have a ton of rock in my tank that sat around dry for months, and after about 6 months you couldnt even tell. after awhile the coraline and critters find their way in. the only concern i would have is if you are adding it to an established tank.
and yes, premium rock usually just means lots of coraline and extra goodies.. but that will develop in time anyway.