This helmet is a modern reconstruction of a second century centurion's helmet. The embossed eyebrows and the circular brass bosses are typical of Imperial Gallic helmets. There are several different styles of Imperial Gallic helmets and it was more than likely a matter of personal preference and/or armoury issue as to what type was worn by a particular Roman soldier.
Most of the helmets used by legionaries had a crest holder. The crests were usually made of plumes or horse hair.
There is some evidence (Vegetius writings and some sculptures) that legionaries had their crests mounted longitudinally and centurions had them mounted transversally.
There is evidence that crests were not used in combat but only in parades, except by centurions who probably wore them all the time.