YYF Shutter Specs:
Diameter: 56 mm / 2.20 inches
Width: 44.40 mm / 1.74 inches
Weight: 67.8 grams
Bearing Size: Size C (.250 x .500 x .187) CBC SPEC Bearing
Response: 19 mm CBC Silicone Slim Pad
YYF Horizon Specs:
Diameter: 59 mm / 2.32 inches
Width: 42 mm / 1.65 inches
Weight: 67.5 grams
Bearing Size: Size C (.250 x .500 x .187) CBC Center Trac Bearing
Response: 19 mm CBC Blue Slim Pad
The Shutter is in the full size category and is 2.4 mm wider than the Horizon, 0.3 g heavier, and has a more straightforward shape having less steps.
The Horizon is in the oversized category and is 2.4 mm narrower than the Shutter, 0.3 g lighter, and has a more complex shape and more obvious steps.
They have completely different specs and shape from each other. They are not that close.