Just do a forum search for Quad cannons and you will get your answer. To sum it up they are not as powerful as XII VR Dual Heavy Phaser cannons. A Fleet Elite or Advanced XII Ulta rare ACC2/CRTH2 will smoke them by far. They also have no (ACC) Modifier so they miss constantly. But they look and sound cool. If you want access to top Fleet gear just go to the Public Service Channel and ask for an invite if your Fleet does not have them unlocked yet.
All you need is the Dil and Fleet marks to buy them and the provisions in your Fleets store. It's worth it just to join any fleet to have access to the gear. Like I mentioned you dont have to buy from "your" fleets store. Any fleet can invite you to their starbase and you can use their store. On the Public Service Channel everything is free also. Just join any fleet go to the Channel ask for invite to Tier 5 Starbase, or Tier 3 Dil mine (for Elite Fleet Armor consoles) or a Tier 3 Embassy (for Fleet Sci Consoles) You can be in a tier 1 fleet and have Elite Fleet Shields and Armor and weapons as long asw your store has provisions. Good luck
They may not be ideal for PVP, but in PVE they're very powerful, and they look and sound awesome.
Also, the Sao Paulo skin for the FTER is actually pretty awesome. I wasn't a fan of the gun placement at first (I much prefer the more concentrated placement of the Defiant class's cannons), but I got used to it... and it's actually pretty nice to be able to actually see the Quad Cannon bolts a little more spread out while playing.
Definitely worth the zen if you like the appearance and fly the TER almost exclusively like I do. If you don't want the Sao Paulo appearance, though, I have a hard time recommending the purchase just for the cannons.
PvP no because they don't have any [Acc] modifiers and they also drain some Engine Power. In PvE they also are not that good. No [CrtH] or [CrtD] just [Dmg]x4 modifier and [Dmg] modifier is the worst modifier in the game.
So no they are crappy weapons only thing good about them is they look good firing from a Defiant class.
I've run the Sao Paulo on my main. And I use the Quads on one of my alt's Avenger. They're not the end-all, be-all of cannon weapons. But they are passable. And more importantly, they adhere to "The Rule of Cool". Especially, if you are a fan of "Deep Space Nine".
Been thinking about the quad cannons tonight and does anyone know why exactly we're not allowed to have more than one of these equipped per ship? Cryptic kind of broke that rule when they allowed us Vesta pilots to put a full set of three on it? I mean, people have already stated that it's not great as far as cannons are concerned with the fairly naff dmg x4 proc so it's not like they're overpowered.