I bought some redwood sinker off of ebay. I haven't used it yet, as it isn't big enough for a concert sized uke (though the auction claimed it was--should have paid closer attention to the dimensions)--I'll have to build a soprano, or put it on a CBU. If nothing else, the wood looks different than anything else on the market, and so, it is unique. There are some claims to improved sound, but as I understand it, it's nothing anyone can put a finger on to explain what makes it "better", so it's one of those subjective things.
I know Hearnes would like us to call for quotes, but I sent in an email stating my intended purposes and how much I'd like (basically a couple inches of quarter sawn River salvaged sinker Genuine Belizean Mahogany, 3' x 9" or whatever they suggest that would get me the same desired result, enough wood for two concert sized ukes).