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The manufacturer does not provide the differences between the two, but they make a very distinct separation between MPN: DA302 and MPN: DA305.
The FN SCAR barrels are pencil-thin profile barrels and do not provide a sufficient shoulder (only about 0.02") behind the muzzle threads for the muzzle brake, flash hider or QD adapter to properly index and align to the bore of the barrel. It is my understanding that the Dead Air SCAR-specific flash hiders are purpose designed to instead precision index and align to the muzzle end surface. There are several other firearms/barrels that are manufactured with similar thin-profile barrels. One that comes to mind is the budget-friendly Thompson-Center Compass--marketed as "suppressor ready" with a threaded barrel--which has caused frustration for myself trying to find a reliable and secure method to attach a QD muzzle device. Dead Air only advertises a SCAR-specific flash hider--there is no SCAR-specific muzzle brake. Caution must be noted that the threading on SCAR barrels is usually longer (at >0.60"+) than traditional 5/8"x24 or 1/2"x28 threading (at <0.60"). This relates to an unknown specification detail concerning Dead Air's SCAR-specific flash hiders and non-SCAR but similar low profile barrels such as the T/C Compass. The Compass barrel I have measured only has 0.55" muzzle-to-shoulder threading. That might be an issue if Dead Air's SCAR-specific flash hider's internal threading is longer, thus jamming into the small shoulder and not allowing the device to thread on completely to properly index and seat against the muzzle surface. There is another option for those that wish to install a standard muzzle brake or flash hider on SCAR-type barrels...that being the utilization of a shoulder ring from someone like Parker Mountain Machine or KBA Custom. Hope this helps.
The FN SCAR 17 flash hider indexes off the barrel crown... instead of the shoulder. This is because the FN SCAR 17 has a vary narrow shoulder. If you have a SCAR 17, You either need to buy the SCAR 17 version or buy the special disk (about $30) that creates a shoulder for the regular version to but up against.