There is a connection between Google (or is it Alphabet) and Bandwidth.com (the Republic Wireless parent company) that I can't quite figure out. Google Voice is mostly based on Bandwidth.com technology, and Republic Wireless and Google Fi are very similar products. Republic Wireless even claims they are about to release a dual-carrier option like Project Fi which they call Tempo.
It is possible that they are just competing, but it seems like there is more of a link there.
I can verify. "Seamless" in this case means "I often don't even notice". If I'm directly watching I can sometimes see it and correlate it to a small dropout but it's nothing that doesn't happen all the time on cell phones anyhow; it's below the noise threshold.
Can also confirm, handover is smooth on republic. The 1GB plan is a little lower than Google Fi as well. 2GB is the same cost as Google, 3GB is slightly higher.
It is possible that they are just competing, but it seems like there is more of a link there.