Both One Block Wonder and Stack N Whack quilts are made by using the repeat in the fabric and layering it to get identical pieces. Most of the One Block Wonders I have seen use just 6 repeats, although the book does tell you how to use 8 repeats, and add corners to the blocks that also use 4 repeats so that everything blends. If a One Block Wonder is done well, you lose sight of where the blocks are, because everything blends from one block to the next and you just see the overall quilt, not individual blocks.
A Stack N Whack on the other hand, uses 8 layers (most I have seen anyway) and uses a background fabric so each of the blocks stand out and you can see the kaleidoscope effect of the layered fabric. I have also heard that with Stack N Whack, you can fussy cut your layered fabric to get the look you want for your blocks, while with a OBW, you cut out all the fabric into your triangles, and that is how you can get it all to blend, because you aren't just picking and choosing the parts you want in your quilt.
So while they both use the same technique of layering fabric and using the repeats you get totally different looks, because of the way you put the blocks together. I know a lot of people use the terms Stack N Whack and One Block Wonder interchangeably, but that is because they both layer the fabric on the repeat, but to me, they are two completely different quilts, and not even close to being the same.
