When I started shooting a bow in the late 70s, endless strings where the norm! Didn't even know that a flemish string existed.
In the 80's, when I started to search for info on them, it was like a long lost secret.
The intial stretch of a flemish is part of the construction, twisting of the bundle, lays, plys, whatever you call them! An endless works against the fibers right away!
I say, learn to build or know at least the construction process of both, and at least know how to serve a string, and enjoy the accomplishment of building what you enjoy, and Shoot the Heck out of it! All good!