It's a full-page ad, not a pop-up. A pop-up is an advertisement that opens a new browser window. A variation on that is a pop-under, which opens a new browser behind the one you're currently using. Those are often designed to disguise the source of the ad.

RCU's full-page ads don't bother me. They surprised me the first time I saw one, because I expecteded to see the topic I clicked on. It was for a product that didn't interest me, so I just click "Skip Ad" up in the upper right-hand corner. It took me about 5 seconds total, which isn't enough to phase me.

You can change the frequency of the ads from the 1 in 25 page views that it defaults to up to 1 in 100 page views. That's 1% of the page views, which doesn't strike me a unreasonable. Being a Platinum Member I could turn them off, but I've left them set at 1 in 25. I've seen some good deals in RCU's advertising before, so it's worth it to me to see them.

For what it's worth, the reason pop-ups are so scorned is that they were abused by so many sites. You'd get browser windows blooming all over the desktop, and you just couldn't stop them. That sort of crap is obnoxious.