Despite your disappointment Theophilus, you have to give Mongoose kudos for saving the Avenger material from being lost to the whole QLI mess.
No. Sector Fleet is more of a background book detailing the inner workings of naval organization - stuff like "Can a Sector Duke give a Navy Admiral an order and expect it to be executed or is it illegal?"
It's good for background material; additionally, it covers the organization and composition of the Spinward Marches fleets, which I don't recall being in the original version. Bought the PDF last night and haven't really had a chance to read it in-depth. I'm definitely getting a hold of the hardcopy when I have a chance.
Pax et bonum,
Dale