I hope I can answer this, since I've upgraded 1 Stars twice!
The original 1 Stars were smaller in size, and had a stainless steel bucket on the side to catch grease (same with the 2 Stars). For 2014 they changed to a slide-out grease drawer (which holds a small disposable aluminum loaf pan), upgraded to a removable plate for making clean-out of the grease channel easier, and added a ash clean-out plate so you can sweep the ash into the grease drawer.
For 2016 they increased the size of the cook chamber to the same as the 2 Star, and introduced the FlashFire Ignitor.
For 2017 they changed the color to all black instead of the silver vein finish, to make it easier to touch-up the paint should you scratch it. MAK also introduced the new funnel style FlameZone, as well as matching new style searing grates & griddle for both the 1 & 2 stars.
Note: MAK offers a FlameZone made & sized specifically for the older 1 Stars, but the newer improved FlameZone will only fit 2016 and newer 1 Stars.