Breakthrough Photography announces more than 20 drop-in filters for Canon's EF-RF adapter: Digital Photography Review
Breakthrough Photography: new ND filters for video and photo by Jose Antunes - ProVideo Coalition
Amazon.com : Breakthrough Photography 77mm X4 6-Stop Fixed ND Filter for Camera Lenses, Neutral Density Professional Photography Filter, MRC16, Schott B270 Glass, Nanotec, Ultra-Slim, Weather-Sealed : Electronics
Breakthrough Photography X3 neutral density filters review - The Gadgeteer
X4 Neutral Density – Breakthrough Filters
Amazon.com : X1 UV Filter for Camera Lenses - Weather-Sealed UV Filter with Protection Against Dust and Water - MRC4, Ultra-Slim, 25 Year Support, by Breakthrough Photography, 77mm : Electronics