My time spent polyphasic was
massively productive. The software and systems I developed during that time formed the foundation of my business. But then I acquired
customers, resellers, contractors, and other business partnerships, which made incompatibility with the rest of the world more difficult to handle.
The other major downside is a distinct lack of flexibility. In a monophasic sleeping pattern, if you have a situation and need to work and/or be on phone calls for 24 hours straight, you can do it easily. In a polyphasic pattern, tiredness hits you like a brick wall if you put off a scheduled nap just an hour or two.
Still, if I was starting a new business from scratch, I would seriously consider going polyphasic again for a few months to build the initial foundation.