I'll preface this by saying that I have not had the opportunity to test the set bonuses at all on the ptr. But at face value I really don't think the set bonus is significant. If the higher ilevel pieces didn't have such poor itemization, I'm not sure I'd even consider getting the bonus.
Perhaps if you're not used to tracking and calling for externals, or If the players you play with are not reliable when you're calling for externals, there is some value add.
The biggest trouble I see with four set is that coming out of last stand you'll want to have saved enough rage for a shield block to chase it. The only way you can really expect to have 60 rage coming out is by not hitting shield barrier for the final six seconds before last stand ends. The only way you can guarantee to have 60 rage coming out is to not hit barrier for the last 9 seconds of last stand.
Both of these scenarios fight against the value of our 4 set bonus. If the 4 set had cut the cost of shield barrier in half as opposed to doubling the size of the shield, it would make the set bonus a lot more playable.
But I mean, that has always been the nature of shield barrier. Deciding to hit shield barrier is often a decision to delay shield block because of the high rage cost tied to it. If there was a minor major glyph that made your max shield barrier 30 rage instead of 60, I'd likely play with it even though it would cut my max shield in half.