I leveled a KDF engineer for an alt and have been flying a Hegh'ta Heavy Bird-of-Prey. It's alot of fun, but kinda ugly. I've been using the Jem'Hadar Mk XI set with Polaron weapons and the 2-piece borg weapons set (I'm still leveling Omega reputation). I was thinking that was a good substitute until I leveled up and got a KHG set.
But, I just did an ESTF and someone parsed it. They said my BOP was doing 10k in DPS. That's on par with my fleet defiant, but not as tanky. It caught me by suprise. I hadn't bothered to parse it myself. I figured why if I'm leveling?
So now I'm wondering if the Jem'Hadar Mk XII would be worth it? Should I stick with Polaron DHCs, the borg 3 piece and get the Jem'Hadar MK XII or should I get the KHG MK XII with borg 3 piece and Anti-proton DHCs?
IMO, The Mk XII Jem shield is an OK substitute for MACO (Adapted KHG) Mk XII, the engines give more power to weapons increasing your DPS a little bit, and the two-piece bonus gives more of a bonus (13.1% for MK XII versus 8.1% MK XI) to Polaron. I'm not a fan of the deflector-- I usually go Positron or MACO myself since I like living more than Antiproton Sweep/Victory is Life for PvE-- but the Mk XII is a decent spec bump.
For KHG, it excels at Torp damage (25% bonus), high capacity shields (though more bleedthrough), and Aux and Science builds(+8.8 Aux two-piece bonus, well-rounded Sci skills in the deflector plus some extra hull). For a BoP, the higher capacity of the Covariant shields might give you a bit more survival than the Resilient type, and KHG have Subvert Targeting Array proc which means enemies are less likely to hit you and has a 20% resist to plasma instead of 10% all energy which helps in STFs since the Borg use Plasma energy type weapons.
As for AP, with the other weapon procs having been buffed, the cost of higher-end Tac consoles for it and the lack of availability of MK XII weapons of that type except Advanced Fleet now, I don't think I'd transition to it unless you plan on Crit-stacking everything (Rom Tac BOffs, Borg console, Rom Console and Tachokinetic Converter Console with being skill'd into Energy Weapon Specilization heavily, plus as much accuracy as feasible for Acc to Crit bleedthrough.) Polaron plus MK XII Jem set is very powerful, a solid option. Disruptor has an excellent proc of debuffing a target's resist, which can boost both your and your team's DPS, making it a good choice on it's own. Romulan weapons are plasma based weapons, but have disruptor procs on top. The two-piece bonus from the Rom weapon/console set is more plasma damage, and the beam of the set consumes 0 energy on it's own and with the three-piece bonus the beam gains a free Beam Overload type ability that also gives large debuff to resists and large plasma burn. Plus, there are now Embassy science consoles that add more plasma damage, making Plasma very, very nice for PvE if you can afford the Dil to get all that and make the Romulan Marks.
If you're using polaron, it's worth it. The damage, power level and flow cap bonus makes it worth it. If you're not using polaron, there's no real point. I do find that even the XII Jem shield is a bit weak for my tastes. I use the engine and deflector with the XII KHG shield ( technically the adapted MACO, as it's on a fed toon) my fed JHAS. On my KHG side tac, I have a bug also, but set up differently (KHG/disruptor).
If you were a science focused player, than absolutely, Mk 12 jem is beyond worth it. (No set is better for a sci ship, or sci focused ship)
But otherwise, it's also good for larger vessels for the buffs in mobility department, without that into consideration, save up for the KHG set for your BoP. Or the Omega Set.
I was using the full Mk 12 Jem space set on my Vo'Quv (Science Captain) and the set goes great with Fleet Polaron Weapons; however, I noticed the Jem Mk 12 shields just seem paper thin when compared to the Maco or Honor Guard.
Running Elite STF my Mk 12 Honor Guards Shields are Beastly and I can keep the shields up with very little trouble but when I used my Mk 12 Jem Shields I was constantly struggling to cover my bare Hull.
I still say getting the Mk 12 Jem Space set is well worth it and if you can pack plenty of shield heals the 3 piece set bonus is quite nice but if you only need the bonus to Polaron weapon damage (13.1%) then the just use the Deflector and Engines.