The other elephant in the middle of the room (at least from what I have seen), is that I haven't seen anyone with any appreciable size who claims to be natural run IF as Lyle suggests and keep any size while leaning down.
Every time I have googled his approach (Search and Images), you come up with loads and loads of pictures and stories of guys who are all gassing and having success with IF.
For kicks, I did some goolging earlier and found the same things to be true of Kiefer's approach. Now, I am not saying that Kiefer's approach won't work on someone who isn't being assisted (there don't seem to be as much evidence of people running this), but just that I am skeptical at best.
So, my personal conclusion on both approaches is: were I gassing and cutting, either approach is likely to support me in my goals of keeping a lot of muscle and losing BF based on the interaction of the dieting approach with the extra muscle-sparing support of the gas. But I wouldn't do either approach as a natural. I'd just hire Rich for diet help.
Complication makes it easy to explain failure.