I've tried this method but as people have mentioned it is pretty oversaturated and you can't find as good offers as before (due to regulations etc). I went from a newbie to slight positive ROI in a week using Monetizer smartlinks and then gave up on popup ads. However, I think it still is a great method to get into affiliate marketing as you get a lot of data for cheap cost, which mean you will learn and improve at low cost. Even if it's hard to get to $xxx/day with pops (still achievable), it's a great step for other traffic sources. Currently running my first facebook campaign with +60% ROI, thanks to the things I learnt from running pops. I'll probably aim for native ads in 3-6 months
Also there's a lot of extra cost you have to take in mind; eg Zeropark and Propellerads had 20% VAT. Voluum is $99 per month for the cheapest package which includes 1 million events per month only. That's very low for pops and you'll probably over exceed that if you're going for $xxx/day, which means you'll pay more than $99 (unless you're going 100% Zeropark traffic, but from my experience other sources were better)