From Madbull, these are fully licensed Daniel Defense style Aluminium outer barrels. Tough, light and high quality; Madbull makes some of the best outer barrels around and they offer them in a broad variety of lengths. A standard M16 has a 20 inch barrel while the standard M4A1 has a 14.5 inch barrel but the beauty of the M16 family is their ability to modify the length with a lot more options then that.
The 14.5 inch barrel is standard M4A1 carbine length so while it may lack the exotic personalization of a non standard length it will certainly be easier to shop for inner barrels. You can swap out to a Daniel Defense barrel without having to affect your internal setup or practical performance at all.
This particular barrel is for standard M4 AEG type receivers, there is another version for the M16 receivers.