I have the shimmering sea shells and love them. It's possible they wear away or dissolve over time, but I love them. The prices really seem to vary.
Mine were $350 for a bag, and I wonder if I got the full bag. I've heard of someone getting them for free, another person paid $100 for a bag, etc. I guess it depends on area, pool builder, and applicators.
I wish I had more, but I probably wouldn't have wanted to pay more.
I haven't really seen a photo that captures their sparkle, so I went on the word from here - glad I did.
There's also discussion about the distribution of the shells in the pool. Some people say they show more in the shallow areas which makes sense and maybe more so with the darker finishes. I don't know. Some people want them mixed in on the walls.
I have Blue Granite and this is where mine are:
Mixed in on the walls
Sparsely hand broadcasted over the rest of the pool - very uneven.
I see them very well in the deep end and love them there too.
What I would do next time:
None on the walls
Buy one and a half bags (but probably not over $500)
Evenly sprinkled over the entire pool
On the fence about adding them to the spa.
There is also an option now of adding a bag of PebbleTec luminous beads to sheen or tec. Check out Ummgood's thread for more info or go to the Pebble tec website.
Suz.