Not quite GCD locked, unless you get really lucky, from my experience. They could bump up the percentage to 30% and it'd be a 100% profitable gain imo.
It's definitely not atm. I'm not getting any procs below 45 seconds from start of proc to start of next proc.
That's the big issue here, still. That set bonus is too good on single-target.
It works for Rallying Cry. http://ptr.wowdb.com/spells/145991-readiness