I avoided popunder for a long time. But then a friend showed me a bunch where popunder gave an excellent ROI. I decided to try it, but the question arose: where to buy it normally, and even for a geo where gambling is allowed? I started digging into the topic. I found an article on the Internet. In addition to networks, the topic of countries where gambling ads are legal is well covered there - it really helped when choosing directions for testing. In the end, everything went better than I expected.