The legend goes that Shimano produced a ‘racing’ pull-chain derailleur called the ‘3.3.3.’ in 1956 and a ‘touring’ pull-chain derailleur called the ‘Champion Speed’ in 1957.
My guess is that this is the 3.3.3.. The pulley cage, sliding rod and spring assembly are the same as on my other Shimano pull-chain derailleur - the difference is the drop-out mounting. In general I consider it to be a copy of a Cyclo design, with one sprung pivot and one unsprung pivot.
This is a competently manufactured component but does not have the class of either the Sanko or the SunTour pull-chain derailleurs. Shimano’s real interest clearly lay elsewhere - with their 1958 ‘3.3.3.’ three speed hub gear.