How well armoured was the Roman army?

[Crispvs]

I recall that when I switched from wearing hamata to segmentata about thirteen years ago I felt that the segmentata, as a more rigid armour, was less comfortable to wear, but I quickly became used to the segmentata. One thing I did notice however was that segmentat was actually harder on the shoulders than hamata, probably because of the way that hamata hugs the underlying body and distributes its weight reasonably evenly, whereas the weight of the segmentata is taken primarily by the shoulders, although this is relieved somewhat by the pressure of the belt at the waist. Until I got myself some padding to go under my armour I used to get very sore patches on my somewhat bony shoulders wearing segmentata.

Regarding popularity, I think that would have a lot to do with what was already available and how a unit was being supplied with replacement kit. We know that some units at least had some sort of 'buy back' arrangement which meant they could keep the equipment of dead soldiers in service for other men for as long as it was serviceable. For new equipment coming into the unit, from the reign of Diocletian onwards there were huge state factories manufacturing kit, but earlier on there were probably numerous private workshops with army contracts to supply equipment. Each of these workshops would probably have its own style or preferences, with one manufacturing one type of equipment and another a different type. In all likelyhood all equipment which had not been allotted to particular soldiers was kept under the care of the custos armorum, who would presumably equip new recruits according to both what he had available and what fitted the individual man's body shape. Personal preference may have had little to do with what sort of armour a man ended up wearing, excepting where a man with a good deal saved up decided to commission something privately.
I think also, and with more relevance to the overall topic of this thread, that there may have been a prevailing wisdom which said that armour (of whatever type) was better than no armour when confronted with weapons of any description. How many soldiers actually had armour though, particularly prior to Augustus, is a better question to be asking.

Crispvs