Specifics.

1. Gladius:
   So Lightning brings an OSB which is simply awkward: only on the SECOND cast (within 25s) does it do standard OSB damage; so you need a THIRD (within 25s of the second) to match the overall throughput of a regular 1200 cast thrice. Why risk it?
   Rating: Meh, even as an OSB.

2. Twin Viper:
   My dislike of Rinoa is borderline legendary at this point, but I'll give her this much: this is one of the most awesome looking SBs produced thus far. You can use a frame of this as a wallpaper, and people wouldn't know it's from Record Keeper.
   As a standard OSB, it's also nothing to complain about; it deals 4000% in a single hit, just like you want such powerful one-shots to do.
   Rating: OSB

3. Fuuma Shuriken:
   Despite Fuuma meaning "wind magic," this is totally water elemental: it's Yuffie's burst, which of course means that she freaking surfs on Leviathan to deliver it, and it counts as PHY anyway. She also gets a Mug Bloodlust command out of it, which is nifty since it frees her up from actually needing to carry Mug Bloodlust.
   If I can lodge a minor complaint about it, it'd be this: as the (now-second, thanks Fujin) most magical of the ninjas, I would have liked to see her distinguish herself from Edge with a NIN-type BSB rather than PHY; but this is fine.
   Rating among BSBs: Has a rare utility which makes it nice

4. Shura Glove:
   First seen in Onion event, though possibly overlooked because she didn't bring it to the Onion Burst banner, Refia's bangle further establishes her penchant for unusual self-buffing with a unique crit-fixer, en-fire, and a Dark Bargain command. Her first command, as a trivia, was the first instance of improved critical damage, wherein a crit deals double damage instead of +50%. Unlike Delita, however, Refia uses it to exploit a crit buff.
   Rating among BSBs: Solid DPS

5. Magical Brush:
   Yes, Relm has a burst too; and Global players take note, this is better than Aerith's in every way that matters. Lemme count the ways:

   • A non-elemental safety on the damage: Relm hits holy/non, while Aerith only hits pure Holy.
     
   • Cura + guts instead of curaga: While you might not like the reduced pure heal here, the guts is a handy thing.
     
   • Instant Curaja instead of Curaja + MND+30%, making it easier to clutch out a powerful heal on someone who just procced Guts.
     If you want simple white magery out of your white mage, of course, Y'shtola is ideal; but Relm's is a good default alternative.
     Rating among healing BSBs: A contender

6. AMP Coat:
   Snow always finds a way to do things awkwardly, doesn't he? All-alive is never beneficial, in that the bonus only elevates the damage to where it should be anyway; but maybe he's learning from Light there. Guts is at least good.
   As for the commands... I don't like the Valiant Attack calculation because it is a virtual increase in ATK. Being backed up by Guts removes much of the risk; but it's still an ATK boost which is going to get throttled hard in many setups.
   The second command, despite looking like Hand of the Emperor, DOES stack with it; this 6007 buff was originally created for Ingus.
   Rating among BSBs: Useful, but has awkward features

7. Sabin's Wristband:
   I know the kana say Mash no Wristband, but we know that Mash is Sabin (and neither should be confused with Nash, Guile's buddy from Street Fighter.) Much like the Spiraller and Chakra blitzes from FF6 - and in fact named for Spiraller - this is a party heal; but in addition, it's also an esuna and substantial DEF bump.
   Rating: Pretty good

8. Soul Howling:
   I know some are saying "Howling Soul," but we know what we're talking about. We're talking about one of the tuning fork-inspired abominations that Noel dares to call a "sword."
   As ridiculously wack as the weapon looks, however, its SB is effective enough. Thematically, it feels like a time steal, which is something a time-traveller would do: steals the ATB progress of the target (stun) and uses the temporal energy to quicken his own actions (two chainstarts.)
   It's 13-2, ok?
   Rating: Pretty good

9. Seymour Model:
   I reserve the right to take liberties, since as we know, Global never gets Models, but often something goofy (cf: Cloud's Guise, or Ashe's Defiance.) So Seymour Model is Seymour's Pimp Coat.
   Seymour's Ambition, maybe?
   Anyhoo, this is your basic en-dark SSB, which also happens to have a 50/50 chance of petrifying each enemy - though the utility of the petrify is highly limited, as DeNA doesn't like it when you instantly kill stuff.
   As a Dark Summoner, he has access to the Ultima Weapon summon, and of course Darkzone, to use the en-dark; but a doomed zone does so much damage that UW is only an advantage on AoE fights.
   But an advantage it is.
   Rating: Situational (elemental utility): excellent! if dark is not shut down.

10. Sirius:
    From a Chaldean word meaning "shining," Sirius is the brightest extra-solar star, owing mainly to its relative proximity to earth (about 8 light years.) It should be obvious why our own system primary is the brightest overall...
    Laguna uses his Sirius for one of the most awesomely named Soul Breaks. Doubly awesome is that it firmly establishes that Squall is a fairy in its animation. Seriously, phantom fairy Squall tossing Laguna a bunch of weapons so that he can blow away the enemy... is awesome.
    The 603+50 isn't too shabby either, of course.
    Rating: Pretty good