I was able to get started pretty quickly. The sign up process and code implementation wasn't bad at all. 5 minutes after I visited the website I was already showing ads on my own website.
I implemented 5 banners in total on my first website, Funny Demotivational Posters | Create Your Own Funny Demotivational Poster FREE. One of them was a lightbox that my AM helped me set up in a couple minutes. Having a personal account manager is definitely a nice touch.
Overall my CPM's are higher than I expected. They are not AMAZING like $3 CPM good but that's probably because I get a lot of traffic from third-world countries.
One of the things I don't like about Qadabra is they have somewhat limited offers to show that are for a very general audience. You'll get typically "spammy" offers, not really niche products. I've seen software downloads, mobile content offers, diet pills, gaming offers, and dating so far. But the CTR and CPM's are pretty good, right? Also, you get paid on revenue share and not CPC. This means if your traffic is junk you probably won't make too much. Only if they make a conversion, but the conversion process for the offers I see are usually pretty easy. I was skeptical with the rev-share model but surprisingly it works pretty well. It also means they'll never have an excuse to ban you.
I make enough with Qadabra among all my websites to make a near full-time living. I see my CPM's have been going up steadily the past couple months so i guess there's some optimization going on over there too. Qadabra pays with PayPal too so it's pretty easy to get paid, but they have other payment options as well I think.
I'd recommend giving them a try. It's really easy to set up and get started. It's not for every website, especially for super niche websites, but if you have lots of traffic and not happy with Google Adsense than give it a shot.