"But the downside is unused space in each block."

That is the trick to their method....first off,  the OS operates independent of the Arrays(erase blocks).....it will organize and in fill every space , contiguously or non contiguously.

For a typical Nand, an array would be 4kbytes..F for a NOR it would be 60k bytes

They have the ability to format and prescribe the whole NAND flash as one, operating independently of the many 4k blocks.

With utility......

doni