I just put on the 5 piece set and I love the proc rate, the shield comes up constantly against 1 sabercat. The problem is the shield did not stop any damage, my hp kept getting hit through it then the shield would go away after 5 seconds. So I am wondering if the shield only blocks damage from other players, if someone has tested it. The set can be seen here, the 5 piece bonus reads as such "Chance to gain a 300 point damage shield for 5 seconds when damaged".
http://elderscrollsonline.wiki.fextralife.com/Buffer+of+the+Swift+Set