I hit a shields down borg sphere once and caused 20k damage. I hit a shields up borg probe once and it did no damage.
There are a number of things that could/should be modified to make this 'admiral-mk X-rare-two day to get' weapon worth it:
1) not shoot downable
2) fly a lot faster but still shoot downable (I like this cause you can use a grav well to vacuum it up)
3) completely drops shields and no kinetic damage when shield is up
4) shorter reload (1min for something that can easily be absorbed by even the weakest of shields is kinda stupid)