iSpyCams

I have a 100 plus domain blog network that I have been lazily, slowly and ineffectively building over the last 2 years, most domains are in the GF niche.

I recently found out about popunders and was wondering what and who's popunder I should use for a test?

Should I make it one that's real close to the site's niche or should it be something more general like cams or dating?

Also, is there actually a negative SE impact for having a popunder?