I like the looks of them and they do seem to add a bit of efficiency to most sizes. I do, however, have a ZPD-189 folder which does a wonderful job of sharpening my Lansky stones. I struggle to get the just right toothieness and tend to not be able to resist reshapening it after only a few days (completely unneeded). The zt100 and Yard Hook are both very tempting designs with the scrapyard being tops with it blade heavy balance. I would love a Busse version but they are out of the price range, especially at secondary market prices.
I have also noticed that quite a few Busse and Busse-kin blades come from the factory with very subtle recurves. My scrapper 5 le is a good example, the edge does not sit flush when put on a flat surface, I was pleasantly surprised by this.