I've been playing around with DB and the other assassin items on Quinn on the PBE since I am a Quinn main.
On live, our common go-to build is GB->DB->Zeal item or triforce.
* The de-warding passive on it feels great honestly, fits thematically and gameplay wise
* The true damage component is nice and useful, but the sound and visuals on it are not noticable at all. I find it hard to use it optimally since I don't really notice it being used unless I look at the damage numbers and my hotbar. I also think the rules for "unseen" are a bit strange to understand - nearsight appears to give it sometimes, but not always.
* I've been rushing this item since it seems to give the strongest 1 item powerspike out of all AD items right now.
* One major complaint I have is that BF sword is a pretty big buy, and it can be hard to save up for making it difficult to rush. I'd love it if the recipe was changed to include pickaxe+longsword instead of BF sword.
* It doesn't feel necessary to build more lethality items after DB which I like.
* Ghostblade felt bad when I bought it. It feels quite a bit worse than it used to. I think it's not tuned properly, and the loss of AS from the active completely removed this as a rush item for me and Quinn has taken a strong hit from that. If you compare the stats of GB to EoN or DB it's quite lackluster.
* The active in general feels a bit lackluster compared to what EoN and DB provide, but I disagree with the idea of giving it an AA block. If I was changing the active, I would probably do something like "Gives 20% ms and your champion is ghosted. While unseen, gives 35% ms." Do something to make this feel cooler or more useful. Personally I'd quite like the return of the attack speed in some conditional form, like "gives 40% AS for 1 second after hitting an enemy champion with an ability" but I am biased towards my champion. There are probably more creative or better things to do here, but I just think something big is missing, this item no longer has an identity.
* I like it, the active seems really cool.
* It's not really visible when an enemy champion is channeling it, which is something to improve on. The spellshield could also be just a tiny bit more distinct, mainly with a stronger border. I'd also like it if there was some color indicator which shows how much longer the enemy's spellshield will be active.
* The stats seem balanced and fair.
* The cooldown on the item seems a bit short, I'd increase it by 5-10s.
Lethality right now doesn't feel tuned properly to me, though I have yet to try it out with the intended assassins. Ideally what I'd want would be the ability to choose between an assassin playstyle and a more marksmany playstyle or a hybrid between the two by choosing lethality items over crit items. As-is going pure lethality just isn't an option for me. Dirk in particular feels a lot more lackluster now. I think it would be fine to give dirk 10 flat pen and have it build into lethality items, since we'd only lose pen after level 3 when doing so since they all give 20 lethality.
I have noticed when facing assassins that they're not nearly as useless when behind and I still need to be careful about them. I have also felt that it feels like when I'm ahead additional AD does more for me than lethality, which is something I'm assuming isn't intended.
I definitely do not agree with giving all the lethality items out of combat movement speed as a stat. It harms all champions which are natural roamers due to movement speed caps, and spreading it around makes it feel like something that was tacked on as an afterthought rather than something considered item by item. If an assassin wants to catch up to a location quickly or escape quickly, they should be made to build ghostblade.
Additional Lethality items:
I think there's a major missed opportunity for a lethality item which grants additional damage towards the enemy champion with the most gold/highest level, or a lethality item/ support item to help with defensive waveclear just a small bit - not enough to take away from dedicated waveclear champs, but enough that the enemy team deciding to group as 5 mid vs an assassin doesn't result in that tower falling before his team can rotate to respond. They would both fill the overall goals of this update pretty well in making assassins less useless when behind, but not extremely oppressive when ahead.
Quinn is a marksman HYBRID assassin according to you folks at Riot, and we at r/Quinnmains agree. Yet she is one of only 3 champions tagged as an assassin to not have recieved any changes (the others being Kassadin and Nidalee). And of those, she is the only AD champion, AP champions are affected significantly less. Personally I feel she leans quite a bit more towards assassin/skirmisher (depending on the build) than marksman just from the way she likes to play the game and the map.
I definitely think the overall effect of the changes to items will result in a nerf right now. I don't think the nerf will be very large, but it will be felt. If you decide to show Quinn some love (which I hope you will), my request would be to contact us as the very first thing before doing anything as she currently has some bugs limiting her power, and there are quite a few changes we would like to increase her power and make her more enjoyable to play than something like +50 base HP.
After continuous testing I've come to the conclusion that my problem with the assassin items was a bit exaggerated here, I think it only needs a bit more tuning to be in a place that it feels good. Late game full lethality feels great and balanced and during the game it also feels pretty nice. The main issue that I've come to realize is that lethality midgame and early/mid feels very slightly undertuned - splitting it to 0.5 0.5 or 0.45 0.55 would probably be enough for me to be happy.
The second major issue is that it still feels like ghostblade is significantly undertuned compared to the other two items. Compared to EoN it gives CDR in exchange for MR, and costs 100g less, but EoN's active is super super useful while ghostblade's isn't quite as effective with all the slows everywhere and lockdown everywhere. Ghostblade needs a better active effect or +5 lethality or +5 AD or SOMETHING. Ghostblade is currently the main complaint I have about full lethality.
I still think Quinn will take a hit and it would be very nice to have some bugfixes and slight changes to make her nicer to play, but I don't think she'll need any number buffs after that. Especially bugs related to Quinn's E have CONSTANTLY been happening on PBE, which is really frustrating.