I've been wanting river stones in TG for almost a decade, but alas, TG just doesn't handle lateral displacement without exponential slowdowns (I hope improvement is seen on things that have been begged for improvement for years over new features).
These are alright. They lack warping to elongate and vary the stone shape but they may look decent from a distance in small masked zones. Regular fake stones used as filler between river stones.
There are also two types of stone distributions to choose from, one based on Voronoi Billows, and one based on Voronoi A noise. Due to size variation between the two, the offset displacements in the Normal and Lateral may need adjustments.