I'm a tile contractor who installed these rocks in my personal home for the shower pan. These rocks are smooth and rounded and have with stood three years of use with no issues. My issue personally with them is I have arched feet and the rock shower pan is quite uncomfortable at first.  My wife has flat feet and loves the feel of the rock from the moment she stepped on them. so the saying goes "Happy ....... "  Like I said it took awhile to get used to but it's a after thought now.