1: Very effective, it's my favorite choke to go for, and not a lot of guys know the proper defense to it when I apply it at my gym.
2: I consider it advanced but the more you drill the technique it becomes a natural motion. I used to try and visualize how I could hit it in certain positions and I would always have to motion with my arms at what angle I'd have to try it, but now it just seems natural to me and I can plan it out in my head with no hesitation.
3: I've recently had a lot of success from side control and North/South. It's the choke I can bait my opponent into rolling right into it. Any type of top sprawl position sets up the choke well too.
I actually just posted a topic on 'How Versatile id your Darce Choke?' you should check out some of the answers.
To me personally it's the greatest feeling when I'm able to pull of a Darce, I've worked really hard at being able to drill this technique and now i'm seeing some results. My BJJ is more fun because apart from just reacting to situations, I'm planning and setting moves up, and the Darce is my favorite move to bait someone into, very rewarding. Now on to the next focus drill, My Mount position. Keep at it man, have fun.