Just asking if it's worth doing Clean Hands for anything other than the achievement, because I don't really feel compelled to let some of the main targets live, but I can easily keep a low Chaos rating.

As I understand it, it is only an achievement. There are some points during the game where you will get rewarded for allowing certain targets to live, and the Outsider mentions one of them, but I do not think it affects the end. I haven't beat the game yet, but I'm led to believe that it is affected only by Chaos level.

Thanks for the answer.. can anyone who has completed the game confirm this?

Sorry I cant help you. I CAN on the other hand confirm that if you get your hands bloody, Like REALLY, really bloody. You get a tremendously satisfactory dark ending.

The Clean Hands ending- is the same as the Low Chaos Ending-

Yep. I can confirm. A little disappointing. I was expecting SOMETHING in the ending to be a shout-out to the fact I killed not a single individual in all my time as a "dishonored criminal". A little congratulations from the guard captains or something. "We wrongly accused you, tried to kill you constantly, but you were so incredibly noble you harmed not one man. We are both shamed and awed at your magnanimous spirit."

Instead, you get one comment from the Outsider if you collect a certain rune in one the later stages, where he basically goes: "I don't understand how you've restrained yourself from killing these men. That fascinates me." I mean, he almost just shrugs his shoulders!

And some of the guard conversations in later stages are completely at odds with what you actually did if you didn't kill anyone and stealthed a stage. "You hear about that assassin in the skull mask? He tore through everyone at the High Overseer's office!" I - what?! By "tore thought" do you mean, ghosted the level and killed no one? After which, the High Overseer was just found branded. And how does anyone know I wear I skull mask?! I've ghosted all the levels! No one has seen me!

It always frustrates me in games where NPC's behaviour is at odds with your actual game-play.

In Skyrim I had guards magically know I was in the Dark Brotherhood despite me not saying a word, and not killing anybody while detected. So much for being a master assassin, eh?

clean hands is just an achievement, what matters is low chaos ending and some decisions like saving "uncle" murrow in low chaos path, and all. If you spare Daud, you get an achievement and on this the outsider comments that he is fascinated by Corvo.
I accidentally killed just one hostile which I later only realized :/ which had some notification :/ now i'll have to replay that whole mission again.

the "good" ending was nice but little unsatisfactory