I can not speak to the specifics for this site. But in general, I would be very very careful about moving from site to site via a pop up ad. there are all kinds of ways a bad guy can exploit you via pop ups to steal your credentials. Its gotten pretty bad, where even legitimate commerce or news web sites have been infiltrated with ads that look like they are from one company but when you follow the details, it really goes to a fake login page established just for the purpose of getting your credentials. easy to imagine a scenario where you have a site where you enter a credit card (like one of those dating sites where you pay to message someone, get heisted and your info is stolen.
I'm not in anyway impugning the integrity of this site, I've never looked at it close. I've just worked on literally hundreds of these situations in my real life. It's a lot safer, if you like the looks of something to go directly to the website yourself, or at the least, watch the URL address of where you are being directed, particularly in credit card situations.