Nail, thanks for an interesting article. You are right about buds. We thought that "bud" would be and obvious and self-describing terminology, but it apparently is not that obvious :-)
And yes, we really did not target block devices, but only raw flashes. There was a project to try UBIFS on block devices. Using it "as-is" will of course sucks, because UBI cannot really utilize the asynchronous I/O of the block layer. This is fixable though, but needs some work. I think the benchmark results would be a lot better in that case.