As a PvE power Reaper I've been abusing the swarm right before I went into shroud so those damage ticks would also get +600 Ferocity boost. Now as life leech;
1. Doesn't crit -> No ferocity effect
2. Doesn't siphon through shroud
I do like the change that it takes half the time to finish the swarm ticks.
Offhand focus is in my opinion lame to use in PvE content (Unless you really need a boon corrupt, even with the change to bouncing scythe skill the damage numbers still aren't that great.