How long is a piece of string?
Kat/Dark is not for the faint hearted. My first ever toon is Kat/Dark and even after two and half years, he's still only 35.
Endurance will be your main enemy as /Dark is toggle heavy and the quick recharging attacks of Kat can lead you to drain your end bar swiftly in a long fight as you'll be smapping them like crazy. As you have no endurance recovery powers, build with +End in mind if possible. Oh and get those -KB IOs fast if you can. With Acro, you'll drain your endurance even faster. There's no synergy between the two sets but they are both very good and in combination can give you come solid defence as well as good resistance to everything apart from Energy. D's still stuck in the RWZ and Rikti pwn him every time I try and play him. Oh and you won't be able to see the nice Kat animations from having Cloak of Darkness on.
On the plus side, you'll be very team friendly and a true boss killer. It's quite possible to run into a mob, disorientate all the minions, knockdown the mezzers and then lay the pain on the boss. Plus, it's very versatile and can adapt to lots of different situations. The heal is absolutely awesome and recharges quickly even if it does cost a ton of end to use and needs mobs around you.
It's a fun and challenging combination, definitely not 'easy mode' and quite versatile. But you will have times when you'll be cursing it as well.
@Dante EU - Union Roleplayer and Altisis Victim
The Militia: Union RP Supergroup - www.themilitia.org.uk
Ty for the poetic help ^_^
I know /Dark is end heavy from my *shudders* Stone/Dark Brute 
I will be planning on slotting Stam with End Mod's and all toggles with End Reducts.
And about the Cloak of Darkness problem; If I can survive without it then I can see the animations 
My main is Kat/DA
Dark Regeneration, and running the soft control = the main end killer. The toggles are actually relatively end-easy. Slot end redux into your attacks
Stacking Divining avalanche & Set bonuses can get over Cloak of Darkness, easy. I still prefer to have it.
Dante is right, however. Certainly not easy. You have to be on the ball and hit dark regen in time, to survive.
Also: don't take both soft controls, you'll tire yourself out :P
Oh yeah, completely forgot about that.
IMHO, I prefer Oppressive Gloom. Less end heavy, more accurate although your foes may wander away from you. Plus if you get Health as a prerequsite for Stamina, it pays for itself. You probably know all this from your Brute anyway but adding in the quick attacks from the sword isn't going to help. Definitely slot end reducers in them as suggested.
Oh and best slotting IMHO for Divine Avalanche is 2 Acc, 2 Def, 2 Recharge and it's awesome. 
@Dante EU - Union Roleplayer and Altisis Victim
The Militia: Union RP Supergroup - www.themilitia.org.uk
Can't coment on kat/dark, but I have a lvl 50 dm/da/dm and a lvl 49 bs/da/dm and one they are IO'd up I never really go bellow 50% end unless I'm spamming dark regen.
I have sacrificed a few % of dmg res by slotting Impervium armors in all 4 rez shields, but it does give a recovery and max end boost.
Have a look at my guide bellow for some /DA tips.
I have a 50 kat/da and it's a great scrapper!
IMO the slow down in damage from divine avalanche, and the restricted defence, makes it of questionable use, but it's definitely a case of YMMV
Mine runs tough/weave, cj and cod, and using only cheaper sets I have 25+% defence to all, and few end problems, plus i don't have to use dark regen so often
IMO EVERYTHING /DA is good
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IMO EVERYTHING /DA is good
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As a man starting my 4th /DA scrapper and a DA tank now i12 is here, I whole heartedly agree.
Just a quick one. Is Kat/Dark good?