In terms of making money it does pretty well, the pay is much higher then what you would make on banner ads (from some ad networks not all) when using site entry script. But the ads are very annoying to say the least and should be used in moderation.
I am not sure how effective they are as an advertiser, my guess is it would be about the same as popunder advertising. It would deliver lots of traffic but the results would probably not be that effective as it is forced advertising. Most people will probably want to skip the ad when it appears unless its targeted correctly.
Another alternative to adf.ly is Link Bucks. They allow you to cash out anytime once you hit $10.00. With adf.ly they only pay once a month.
Adf.ly domain has been banned from India and some other countries. so I wouldn't try to use adf.ly if you have asina trafic. I would suggest 'Direct Link' and Popunders by edomz. They are known for higher cpm and i have been using them from past 2 year. Payments are always on the time and it's a pleasure working with these guys.