Fourth Cuirass  

Since no one has posted, the "Increases HP" does the following:

1 piece: no benefit
2 pieces: HP+10
3 pieces: HP+20

I didn't bother getting the 2 other pieces because my 55 pld was wearing boots for shield skill and gloves for enmity. I can guess that the other pieces would've been HP+10 if put on but the boots and gloves for pld af has more hp on them. I'm uncertain if all 5 pieces would have a "full" set bonus but it might be possible but was pointless to find out on my pld. Hope this helps people to determine if this set is worth it.