Actually, that ship and the Guardians. Radiance forces the bulk of the fire onto it, the Guardians absorb some damage. Negates an enemies ability to focus fire. When you want to, you can use the Guardians to put them into a corner. That would be a bitch for a a typical LRM/Repair fleet.
Guardians most of all I think. I mean if you've got a dozen of 'em in a fleet, it's not exactly beneficial for them all to use their repulsion abilities at the same time. That said, thus far I've been too lazy / busy to micromanage my Advent ability usage.