While SB has been described as a "cousin of the Zone diet, there are some very major differences. SB has phases, which vastly differ from each other in regard to their effects on the body. Phase 1 shocks the body by putting it into ketosis, not a healthy state (note that SB limits Phase 1 to no more than 2 weeks; no surprise!). Phase 2 adds back too much carb for you to be able to maintain favorable hormonal responses (specifically lower insulin levels). Phase 3 is put into practice once you are at you goal. To sum that up, it's basically saying 'ok, by now you should have learned how to eat so go of it on your own, and when you gain weight to the point you are becoming overweight again (and you will gain again eating that way), go back to Phase 1 and 2.' IMHO, there you have it, the definition of yo-yo dieting.
I highly recommend reading TOXIC FAT to gain a full understanding of all the benefits of the Zone.