I think it depends on what source you read,but the segmenta started to fall out of use in the Late second/early third century, I am sure I have seen a website, the Roman army website one(?) Where there are examples of third century segmenta.So I would use these figures for the period stated.You could always mix in some figures from the A&A miniatures Middle Imperial Roman range to suggest the Legion in transition.
Some symbols were attached to the various Legions but whether they were used on shield designs is unknown.
Sound advice regarding A&A. For later 2nd century you might also take a closer look at Aventine's period-specific range.
With Victrix' EIR devil's in the details though. Yes, there's evidence for laminated armour in use during the 3rd century. However, these types looked different. The Victrix legionaries seem to wear Corbridge-style armour, which is commonly dated to the (late) 1st century AD. Soldiers of the 2nd and 3rd century would rather use Newstead-types or variations thereof (larger plates and hinges).
But even if you ignore such relatively minor issues, in sum sidearms, caligae, and the use of Weisenau helmets put this set firmly into the – very broad – 1st/2nd century bracket.
Again, this shouldn't trouble anyone using this set for earlier or later periods. It's just not as 'accurate' as it could be.

PS: For a 'genealogy' of Roman helmets I recommend
this overview.