FF is agile, FFB is not, so you'll probably find the FFB outmaneuvered by its squadronmates. The SFU has "leader" variants of most ships. These leaders are intended to lead squadrons of similar ships as part of the battle group. They have a bit of extra shielding and a few extra phasers, plus command facilities. (I hope we shall see statlines for these at some point in the future...)
In the SFU canon, during the General War combat was so intense that frigate sized ships were dying in droves. As a result, all empires started beefing up their small ships. The Feds designed two: the battle frigate (an upgrade to the frigate) and the war destroyer (new design). Two FFBs were built historically IIRC. The FFB was found to be too small and cramped, whereas the slightly larger DW got the nod. Prior to the war, the FFBs were assigned to the Romulan border fleet which was considered by the Federation not likely to ever see any combat.
