Before we look at the rules and use, let me just say the hobbyist in me really likes the model and I have ordered one nevertheless. A few magnets here and should suffice to switch all weapon types.
With all these weaponts being AP4 or worst it has a limited damage output, nowhere near a true AI specialist like the Helldrake that can decimate a squad per turn. And this is where the key of the issue lies - where a Helldrake is designed to operate solo, speeding forward towards a Troop unit in cover (probably sitting by an objective), the Dark Talon moves with the rest of the Ravenwing, adds its dakka to the rest of the spearhead to force saves rolls, and uses the stasis bomb to give the RW chargers a significant combat advantage - attack before it's MEQ opponents and hit them on 3's. Its Hurricane Bolters can also benefit from the Retribution Standard and dish out 24 twin-linked shots, but this is too unreliable to count on it. It can hover though, and benefit from an improved jink save of 4+ if near a Dark Shroud and especially from the saturation of objectives. It isn't especially killy so your opponent might just prefer to shoot the bikers, especially if they are scoring - and very often they will be through Azrael or Sammael.
Is it worth the 160 points? I would say no. A similar damage output can be achieved by adding more bikers, terminators or simply a couple of Predators. And the Ravenwing Grenade Launcher can create similar advantages. That said, it is not as bad as some have put it and can have it's place in many lists.
If equipped with the Avenger Mega Bolter it gains some AI duality, supressing the enemy with 10 S5-6 shots (5 Avenger, 3 HB, 2 missiles per turn during 3 turns); for some reason GW has kept the main gun and missles only AP4 so again has a limited damage output. When considered in the context of the army, well again these are wounds that stack up with the TL botlers of the bikes or the storm bolters/heavy weapons of the terminators. The army can also have plenty of AP2 weapons to deal with MEQs/TEQs.
As an antiair platform, it is somehow disappointing. First of all, the TL lascannon will hit 9/10 times (roughly) and cause an internal hit 50% of times vs. AV11. The other 4 S5/6 shots can help getting additional glancing hits. As for the internal hits, its FP2 and can substitute a weapon destroyed resul by an inmobilized. So yes, it can take down a flyer but it can also just take a hull point or two and leave it still functional. Now again, there should be some more AA in the form of quad gun and flak missiles to help take it down.
Wait what about the points cost?There's wide consensus in the Vendetta being severely undercosted, but even the comparison with the Storm Raven, a 200-250 points beast, is not good. For 30 more points the Storm Raven has better armour, better weaponry, PoTMS and the capacity to transport 12 units plus a Dreadnought. More often than not this is not a good idea but at least the 'Raven can do it. And it has an assault ramp. If we were to use the Storm Raven as refernce and reduce its point cost as we strip these upgrades, we would very likely end in Vendetta-levels of cost. As it stands now, there's nothing in the DA flyers that justify their currents points cost. Let's see what happens with the rumoured Dark Eldar and Tau Flyers coming soon.
ConclusionThe expectations were certainly higher - hopefully not to be as broken as Night Scythes are but to be more deadly like Helldrakes are. The DA Flyers are not killy by themselves and what is worst, don't really add anything that the army has elsewhere. Top it with a high points cost for what they do and the result is, it is difficult to justify their inclusion. The firepower the DA flyers dish is merely acceptable, and they pale in comparison with their imperial counterparts.
In tournament games it is not a lesser factor that the flyers have to start and reserve to enter the board alter. Many times the more you will play is 5 turns, further diminishing the return of your investment.
To close, I wouldn't go as far to say they are unplayable; they are useful after their own fashion and fit well with what the rest of the army do, so please go and field them if you like their look, fluff or just because you own the model. But efficiency-wise I would be tempted to invest the points somewhere else.