[Al Skierkiewicz]

Brandon,
Are you asking if these are legal for use in the Wago terminals? If so, there is no rule against it. However, these are not recommended by the manufacturer. Stranded wire in the Wago terminal is expected to flatten when the Wago terminal is allowed to close. This causes a significant increase in the surface area of the wire promoting low contact resistance and less heating. The only ferrule recommended by Wago is predictably a Wago product which has a rectangular cross section.
It is for the same reason, I recommend that team DO NOT TIN wires for use in the Wago terminal blocks. Any procedure that forces a round shape to anything inserted in the terminal reduces the contact area to a fraction of that achieved by bare wire. This significantly raises the contact resistance. For that reason I recommend you do not use solid wire or any of the terminations discussed above.