I'll also put in a NO for those calci-sand substrates. The only one that holds any appeal to me is CaribSea's Reptilite. Otherwise, I usually recommend a fine silica-based sand, such as Zoo Med's Repti-Sand. Though personally I use play sand :P Never lost anything to impaction yet.

I am of the opinion that a lot of impaction issues are more related to proper hydration, but I never did like the way Calcium substrates stick together after they've been wet in the first place.