Just a quick question that hopefully someone with some experience with pop-under's (popads.net in particular) could answer. If the LP pops under the users current window / tab. Does the load time of the page really matter that much since the page would not be visible to the user? Or do these pop-unders work differently than I'm envisioning ? I can see for example with pop-ups how the load time would be critical, but I'm not able to make the same connection with pop-unders. I've done some spying (manually) in different geos and so far I have not been able to trigger a pop-under ( just popups) so starting to question my own understanding of how pop-unders are actually displayed to the user. Does anyone have any insight here ? It's a question that has come up during my LP load time tests...carrier traffic in particular.
Actually page loading speed is key to get profitable on Pop traffic in general. It doesn't really matter if it is a pop-up, pop-under, new tab, new window or whatever way your landing page or direct linked offer is being served.
With that being said, if your page doesn't load fast enough and you have a pretty strong angle that would make the visitor click and convert on that offer you just missed a valuable conversion in a probably profitable placement. On top of that, nowadays users are pretty fast while interacting with their smartphones or tablets so the time window you have to attract their attention minimizes again.
Regarding manual spy through behind a vpn or proxy service there are several technical factor to consider like VPN/Proxy delays (the route that the camp you're spying will have to pass through); the landing page you are manually spying may be optimized through CDN on another geo and finally your own connection speed. By combining all these together the result is pretty clear 
Thanks for the response! I will take your word for it that page load speed even for pop-unders is critical. I just still don't understand why. My reasoning goes like this: If the user doesn't see the page pop up, then what difference would it make if it takes 10 - 20 seconds to load? If it's all happening behind the scenes and does not interrupt the user's browsing experience, then I just don't understand why it would matter. I'm sure I'm missing something (probably at the technical level) on why this is the case! Anyway, I'll be content to just take you at your word that it matters, even for pop-unders. I certainly do want to have fast landing page, so either way I will optimize that. Thanks again for the response!