I'll be adding my review notes below the unboxing video.
The 54 is available through One Drop and on YoYoExpert
Here are the specs:
Diameter: 54.00 mm / 2.13 inches
Width: 40.9 mm / 1.61 inches
Gap Width: 4.34 mm / .17 inches
Weight: 63 grams W/ Aluminum Spikes
66.4 grams W/ Brass Domes (domes were included for a while as a promotion at YoYoExpert)
Bearing Size: Size C (.250 x .500 x .187) One Drop 10 Ball Bearing
Response: Flow Groove
Here's the unboxing vid...