The designer of the Brownell's screw did not appreciate Marlin's purposeful design and assumed that it was a standard SAE conforming fastener.
You can trust Ranger Point - they produce fine quality and STAND behind their products. They UNDERSTAND the nuances of gun manufacturing.
Personally, I prefer a more compact straight knurled coin slotted screw that can be easily tightened. Ranger Points screw allows superior finger grip by design.
Marlin's .210 Diam X 28 NF 2A is an undersized #12-28. Gun manufacturers do such things to prevent folks using cheap fasteners that could lead to a safety issue.