Well this caused a bit of confusion when it was announced, "Wait isn't there already a Phase I Clone Troopers Expansion???"
But on closer inspection this is a Clone Trooper UPGRADE expansion, where-as the other is a UNIT expansion. The same goes for the Stormtrooper, rebel trooper, and B1 battledroid UPGRADE expansions that were announced at the same time. SO these are more specialised units that can run as their own unit or "enhance" the regular unit.
The Galactic Republic’s Phase I Clone Troopers are always armed with state-of-the-art equipment. For most clone troopers, this means carrying the powerful and versatile DC-15A blaster rifle, but a select few Phase I Troopers are trained in the use of even more weapons, ensuring the Grand Army of the Republic is prepared for any situation.
The Phase I Clone Troopers Upgrade Expansion contains four unpainted, finely sculpted soft plastic Phase I Clone Trooper miniatures to enhance your existing Phase I Clone Trooper units or to form one corps unit, along with new personnel and heavy weapon upgrade options.
This Phase I Clone Troopers Upgrade Expansion for Star Wars Legion is due in Q4 2019.
Dark Star Games - The UK's best pricing on the Star Wars Legion miniature game