I'd guess the downside to the electric xfer pump is inability to control speed. It's either off or wide-open. If you are controlling flow w/some ball valve, then pump will be building a lot of pressure against the valve. I guess I find myself often throttling back gas pumps in many situations. But, maybe you need full bore & it will work for you.

You are talking about 1ph motors...right? I think most all smaller generators are 1ph.