I don't like the idea of the orbs being lost due to heavy movement fights. I haven't delved into any 5.2 fight mechanics yet but I can think of plenty of T14 where it wouldn't be the most thrilling bonus.
Pretty sure someone posted in another thread that 50% uptime on EB wouldn't be likely even in T15 gear. Who ever math'd it out is probably lurking.
Still a great set bonus as it rewards us for using an ability we should already be maximizing. The 4P is a bit ambiguous to calc.