I haven't tried them, but I was tempted to buy them a few weeks ago when I was researching stones online-- mostly because of the beautiful storage box! What a silly reason to buy, I know, but it's very pretty.
Since I haven't used them myself, I can't add anything in that respect, but what I can say is that stones are so expensive! Like, silly expensive. I wound up going to a local rock supply store (landscaping supply places do this, too) and they had giant piles of river rock to go through. So I spent a few hours digging through and finding basalt stones that were smooth, uniform, no cracks or rough edges, etc. It was a blast! I think the guy charged me $1 for about 75 stones. Not all were usable, but for $1, I can't complain. Once I got them home, I soaked them, scrubbed them, then boiled them and did the seasoning thing. Out of all that I picked out, I got 30 or so usable stones, many of which were nicely matched pairs. I know this isn't the route for everyone, but I had a ton of fun finding my own stones and they have a lot more meaning to me since I found them myself instead of buying them.