I have purchased from them a few times, and have been satisfied with what I received. Personally, I like to hand pick the rock I am going to use, as I usually draw out plans of the tanks and will look for the "puzzle pieces" I had in mind, but if you are not as anal as I am, lol, then go for it.
One thing I suggest though, is Ordering by phone, speaking to an operator. That way you can state the size of your tank and have him/her note that on your order, so that when it is filled, you won't end up with a gargantuan piece of rock, or a million little ones.