The Stellaris API has been used by thousands - thus has long been proven. And - it often achieves multiple Register set-ups/configs - via a single API function. Neither holds true for Direct Register - thus you, "cull yourself from the herd" - unwise on the Serengeti - perhaps this sometimes hostile plain as well...
In addition - many (most) of the API functions include, "built-in" bounds testing - and will "squawk" when you enter an incorrect parameter. Direct Register usually provides no such, "safety check."
There are occasions where you must use Direct Register - due to the API not covering each/every Register, "nook/cranny." (vastly expanded PWM capability - in M4 devices - is one example, the "unlocking" of certain critical MCU pins - another) And - when used correctly - under certain conditions - Direct Register may reduce code size and speed execution...
Be aware that ARM MCUs - from any maker - are highly complex - and considerable understanding, mastery and proper exploitation of Direct Register will enforce substantial investigatory time/effort upon such users.
Employers usually expect/enjoy "quick" results - far more likely from those using the rich, robust Stellaris API. (and hopefully from the rebrand version - which vendor saw fit to modify - and evidences some misfire at this point in time...)
Your green "tick/verify" may reward this in depth, considered, week-end response...
