And I can clearly see why lawyers do not recommend switching from AOS to CP. For starters, it adds a few months (might be 6, perhaps more) to the waiting time because the file has to be physically moved from a service center to a consulate abroad. Secondly, this physical movement is what scares me the most, because the file may be lost so easily in the process. And last, but not least, you effectively become ineligible for AOS benefits such as AP and EAD.
Is it worth it? Definitely YES! But not at the point when you have already waited for a year for your AOS to come through. Especially, if you have voided your H-1B already by working on EAD.
And remember, there is no AC21 for CP.